Thanks, @torohill

* Reindexing did not properly flush the last batch of items to the search
  therefore reindexing would always miss the last few items.
* Creating a new html thread entry with inline images resulted in empty
  search content
* HTML tag stripping in HtmlThreadBody::getSearchable() would result in
  missing white space between some words, resulting in poor searchable
  content

Several mail clients do not return the Message-ID header in a In-Reply-To or
References header as they should. The assumption by such mail clients is
that the email be threaded based on the Subject header. However, osTicket
does not require the ticket number to be placed in the Subject header and so
has trouble threading email from such systems. osTicket embeds a copy of the
Message-ID header (or compatible version) in the body of the message in
hopes part of the message will be returned.

Many mail clients (such as osTicket) strip and clean the HTML when
processing HTML email. Previously, the message-id token was embedded in a
@data-mid attribute, which was likely stripped before the HTML email would
be returned back to osTicket.

This patch suggests that the token be placed in a @class attribute, which
has a much better chance of returning to osTicket.

The %ticket_email_info table needs an index on thread_id. This is done in
the `develop-next` branch; however, this patch helps alleviate performance
issues on the main branch until the `develop-next` branch is collapsed for
main line development.

If the system receives an email by a collaborator which has not yet been
added to the ticket (a friend of a friend — that is, a collaborator forwards
an email to a third-party), a header is added to the thread body something
like:

Received From: afriendofafriend@mycompany.tld

However, if the thread body is text and the HTML ticket thread is enabled,
then the text formatting hint will be lost and the body will be assumed as
HTML deeper inside the thread entry creation process. Therefore, the
whitespace inside the resulting thread entry will be collapsed.

This patch addresses the issue by maintaining the original format hint with
the thread body.

Also try harder to send a relevant In-Reply-To and References header back
to the client with the email message.

This script adds a single download script, 'file.php', which provides access
to files of all types to all users. It uses a HMAC signature system with an
expires time, which allows signed URLs to be sent to external users.

This also fixes an issue with the Http::cacheable() method, where the
last-modified and Etag headers were not properly compared, which resulted in
permanent cache misses by the client.

Stop trampolining links via l.php. It was necessary before in order to avoid
the potential of leaking ticket number & email. The authentication mechanism
in place now redirects on successful login.

This patch changes the default formatting for text bodies used in emails,
ticket thread, and canned response quoting so that white-space in text
bodies is properly preserved. Previously, the text was treated as raw HTML
and was not properly escaped, nor was the original whitespace preserved.

This patch suggests a change to the message-id creation process that
includes stamping the receiving user-id (staff or client) along with the
thread-id of the originating notice. This allows detection of threading if
the clinically brain-dead mail client drops all the other header detection
mechanisms, including the tag placed in the email body, on response.

This patch works for both client and agent communication.

The ticket number regex was changed with the advent of custom ticket
numbers, and it matches the closing punctuation in [#12345], that is, the
closing bracket would be included in the ticket number sought in the
database. Therefore, it would never match the ticket number properly.

The new regex attempts to match punctuation and non-punctuation groups so
that punctuation in the middle of the ticket number is matched; however,
punctuation at the end is not. So #12345+DEPT will match properly and will
ignore any trailing whitespace and punctuation.

Previously, the code would scan the email headers until it found a positive
match from any of the email headers scanned. Additionally, it would attempt
to find the user from the tagged email references header. However, this
algorithm assumed that the references header was constant and predictable in
its ordering. Recent tests with Gmail prove otherwise in some tests.

This patch changes the system so that only the tagged reference header is
included in the References header, and it will scan all items in a header
(namely the References header) until both the thread and a user are
identified. If a user can be identified, the thread and user are returned.
Otherwise, the first thread hit is returned.

Also, fix duplicate emails where a user as a collaborator would be sent a
confirmation for their own respective email.

Attachment settings are now exclusively handled by the settings on the
ThreadEntry field on the ticket details form. Enabling attachments as well
as tuning attachment validation settings are all handled from the one place
now.

Ticket numbers are now configurable as a system-default and by help topic.
Previously, an administrator could select between six-digit random and
sequential numbers. Now, the sequence is selectable so multiple sequences
as needed, and a format can be specified to define how the ticket numbers
look. Formats can also be defined for each help topic.

Multilanguage Support via gettext

- added gettext encapsulations to all texts i thought necessary
- added fallback function for the case that the gettext extension isn't loaded
- added browser language detection
- added gettext to the list of optional extensions in setup
- rewritten some of the texts to use sprintf instead of appending strings
- added german translation file
- removed mark_overdue-confirm from cannedresponses.inc.php

extend multi language support and a fex fixes

- Better detection of translation files
- Added functionality to redirect language codes (see redirecting
language codes)
- Ticket Status can be translated
- The Datepicker can be translated
- Extended functionality of 'testlang.php' to show what language code is
used to translate

Forgotten to apply a patch from RC5 to RC6

- Forgotten to change $var to $vars in line 380 of class.mailfetch.php
- Removed unneeded comment

Added php_gettext as primary translation engine

- Added php_gettext support (thanks to Danilo Segan and Steven
Armstrong)
- php_gettext is now the primary translation engine
- Extended language detection functionality

Add error/misconfiguration checks and fix undefined variables

This will be useful for plugins which might need to scan the message body
regardless of its encoding. This will also be required for full-text indexes
which will not need to index HTML tags, for instance.

This patch adds an 'email' format to ThreadBody::display() which allows
formatting the html/text bodies specifically for email. Previously, there
was ambiguity between the html view (which included inline image support and
clickable links) and the email view, which requires neither.

If an email contains both inline and separate attachments, the previous
logic would detect all the attachments as inline.

Separate attachments have the `cid` set to `false`. This will pass the
`isset` test, which would cause the logic to search through the body for a
string of `cid:`, which would very likely be found if there was another
inline image somewhere in the body of the email.

With the advent of 1.9, the original, plain text email is saved in the
thread table. If a system has the HTML ticket thread enabled (which is the
default), if the plain text message is placed in the email template (which
is always HTML), it will not be formatted as correct HTML and the whitespace
will be collapsed.

This patch addresses the issue by always returning HTML from the asVar()
method, which is used to embed the thread post into a email template.

This occurs for attachments added via the staff or client web interfaces