This patch partially reverts the previous database migration patch which
added a primary key to the table on the `thread_id` column. This column
cannot be used, because there may be multiple entries for thread_id = 0.

This also allows ticket_collaborator.isactive to be negative, as well as
adds the database portion of regex support for ticket filters.

Add the current backend to the list results output
Add a --limit switch to support limit results sent to a command like
`migrate`

Allows for backend listing, file listing, single file dump and file
migration.

Allow arguments to have sub-command 'options', so an argument like 'action'
can have a specified list of values, each with respective help output.

Add `attrs` field for backend state information (multi-part migration,
multi-part upload, etc). Change `size` to be an integer rather than text
field. (Storage space will be about the same, but int makes more sense).
Size the `key` and `signature` for ~512 bits. The base64 encoding allows
6-bits per char. At 86 chars, we have 516 bits maximum space.

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

Conflicts:

	include/upgrader/streams/core.sig

And install initial data in target language. Also configure help tip
popovers to be in the configured, default system language.

Starting with v1.8 osTicket will require mysqli extension.

This patch allows for the specification of a socket in the database hostname
field, such as localhost:/path/to/mysql.sock

This includes the initial concept of pluggable authentication along with the
initial concept for a plugin management system.

line 199: in case of custom upgrade streams, variable $signature contains the last value from the foreach cycle at line 130, not the core schema signature!

line 209: if we do not insert schema signatures for each custom stream, after install osTicket thinks it needs an upgrade and gets stuck (see function isUpgradePending() in class.ticket)

Allow the php source analyzer scan for $this in static functions as well as
properly handle the exception variable inside catch blocks.

And freshen up the upgrading guide