Fixes the rewriting of the `key` field in the ticket thread body. The
storage de-duplication system may replace the `key` value with an existing
one. The ticket thread system will use the `key` value assigned when the
file is committed to the database or the existing key of the duplicate file.

Also fixup installation issues with the attachment storage plugin
architecture

  * Include a `bk` column to store the storage backend
  * Include a `signature` column which represents a repeatable hash of the
    file contents
  * Rename `hash` to `key` since it isn't a real hash

Move the cacheable code to the Http class and allow the client configuration
to be cached in the browser

Previous explain included a nested sub-select, which exponentially increased
the count of the rows to be examined. This patch eliminates one layer of
nesting on the sub-select and dramatically increases the performance finding
orphaned files.

Fixes #773

References:
http://www.osticket.com/forums/forum/osticket-1-7-latest-release/troubleshooting-and-problems-aa/9446-version-1-7-much-slower-than-1-6

Including adding support to the TCL uninitialized variable reader to ignore
class-static variable access as well as detect inline functions and their
closure arguments.

Process inline attachments in thread entry and support inline images in
piped emails

Support inline images across the system, with draft support

Migrate to a single attachment table
    That way we don't need a new table for everything we need to attach an
    inline image to (like a signature, for instance)

Add richtext support for internal notes

Implement images on site pages

* Image paste in Redactor
* Make non-local images optional
* Placeholder for non-local images
* Fix local image download hover
* Don't re-attach inline images

When scanning the file_chunk table for orphaned file chunks that can be
deleted, apparently, MySQL will read (at least part of) the blob data from
the disk. For databases with lots of large attachments, this can take
considerable time. Considering that it is triggered from the autocron and
will run everytime the cron is run, the database will spend considerable
time scanning for rows to be cleaned.

This patch changes the orphan cleanup into two phases. The first will search
just for the pk's of file chunks to be deleted. If any are found, then the
chunks are deleted by the file_id and chunk_id, which is the primary key of
the table.

The SELECT query seems to run at least 20 times faster than the delete
statement, and DELETEing against the primary key of the blob table should
be the fastest possible operation. Somehow, both queries required a full
table scan; however, because the SELECT statement is explictly only
interested in two fields, it is more clear to the query optimizer that the
blob data should not be scanned.

References:
http://stackoverflow.com/q/9511476

Previously, filenames saved in the database had the spaces changed for
underbars; however, other characters (such as commas and non-ascii
characters) presented issues with user agents downloading the attachments.

This patch handles the filename encoding for two special cases -- internet
explorer and safari, and provides the semi-standard RFC5987 method of
encoding the filename for the remaining browsers.

Attachments are no longer forced to be downloaded. It is up to the browser
to decide if the attachment should be shown in the browser or downloaded.

This patch also fixes a slight bug in the caching mechanism for downloads
concerning the last-modified time. The date sent to the browser was not
properly converted to GMT time, although the server claimed that it was.

Previously, filenames saved in the database had the spaces changed for
underbars; however, other characters (such as commas and non-ascii
characters) presented issues with user agents downloading the attachments.

This patch handles the filename encoding for two special cases -- internet
explorer and safari, and provides the semi-standard RFC5987 method of
encoding the filename for the remaining browsers.

Attachments are no longer forced to be downloaded. It is up to the browser
to decide if the attachment should be shown in the browser or downloaded.

This patch also fixes a slight bug in the caching mechanism for downloads
concerning the last-modified time. The date sent to the browser was not
properly converted to GMT time, although the server claimed that it was.

The "ft" field does not exist when the attachment migration takes place.
Therefore, attachment migration will fail because the records cannot be
inserted into the database due to the missing "ft" field.

Administrators are allowed to upload one or more logos and then select from
the uploaded logos to set one for the client site. Logos can also be deleted
on settings->pages submission

Looks like a long standing, yet-to-be-fixed PHP bug, where
zlib.output_compression can result in the output buffer not completely being
flushed. This is especially critical for downloads where the tail of the
file might be lost.

https://bugs.php.net/bug.php?id=19436

This will remove the upper limit of BLOB sizes imposed by MySQL with the
max_allowed_packet setting completely.

This adds a new table %file_chunk which will contain the filedata in smaller
chunks (256kB). It also includes a new class, AttachmentChunkedData, which
will handle reading and writing the data, abstracting away the chunks.

This is done by migrating data from the %file table to the %file_chunk
table. One must beware that this must safely (the migration that is) plug
into the both the live osTicket developers as well as the users doing a full
upgrade from osTicket-1.6*. For this, the AttachmentFile::save method was
patched to use the new AttachmentChunkedData class to write the attachment
data to the database in chunks. That is, the migrater will use the new code
on the major upgrade and bypass the filedata column of the %file table
altogether. Therefore, the patch associated with this commit will not
migrate any data for the major upgrade.

For developers doing incremental upgrades, the patch included in this
commit will transfer the data from the %file data to the new %file_chunk
table by chunking it. As written, only the first 16MB of the attachment is
migrated. This could easily be adjusted, but it seems like a reasonable
limit for now.

MySQL is kind enough to quietly truncate the filedata field when attempting
to CONCAT data beyond the size of max_allowed_packet. The simplest fix is to
automatically adjust the max_allowed_packet to the size of the file being
uploaded plus some extra. See MySQL bugs #22853, #34782, and #63919 for more
discussion on the issue.

The max_allowed_packet variable default to 1M, but is expandable to 1G.
Therefore, the fixed limit of attachments for osTicket will be 1G, since it
would be impossible for MySQL to append data after that mark. *Sigh*

MySQL has a limit on the maximum amount that can be transferred in one
statement. It's the max_allowed_packet setting. The value of this setting
will be the approximate upper limit of attachments that can be handled by
the database given the current access model for osTicket.

The issue came up for attachment uploads and was corrected, so that uploads
are chunk inserted into the database. Downloads, however, were forgotten.
Strangely, it took quite a bit of debugging to track down the problem.

This patch corrects attachment downloads by fetching 256kB chunks of the
attachment at a time and sending them directly to the client. This will also
overcome PHP's memory limit which would be the second-level blocker of
attachment sizes. Lastly, the AttachmentFile::getData() method is simulated
using output buffering. This will provide the same access as the previous
getData() method; however, it is still subject ot PHP's memory limits.

This overcomes the eventual limit of and database to support queries of a
finite length. We now split the file contents into 100k chunks and append
the chunks to the database one chunk at a time.

Also add a cron job to perform the task on demand
Change the implementation for Ticket::deleteAttachments to call this method
after simply removing all entries from the %ticket_attachment table