Update class.mailparse.php

Best version of https://github.com/osTicket/osTicket-1.8/pull/348

static keyword added to enable strict test mode.
Update run-tests.php

Allow tester to run single test by specifying it on command line: php run-tests.php TestMyThing etc.

Still works for normal tests.
Create test.header_functions.php

Creates a regression test for the parsePriority function, as suggested by GreezyBacon https://github.com/osTicket/osTicket-1.8/pull/348#issuecomment-31326865
Brush up import concept to be more flexible
Implement file content loading
Write new signature on file data loading
Move transfer and transfer_array to DatabaseExporter
export: Add new tables for osTicket 1.9
config: Save integers for autoresponder config
Ignore internal importers
Ignore internal importers
If you're logged in as a client, stay that way

When following a link from an email, if you are already signed in to the
help desk as a client, you should just be redirected to the new ticket.
Only ticket owners can update ticket details
Pre fill user email address on sign-in page
Add more emphasis to the subject line
mail: Add signals to interact with mail processing

Signals added:
  * mail.received
    Called after the mail is received into the system and before it is
    processed by the mail system. This signal is useful to do header
    injection. Raw message/rfc822 included in 'raw' key in the info

  * mail.decoded
    Called after the initial decoding of the message. The header and bodies
    are broken out, however, Unicode decoded may not have been performed
    yet. This signal is useful to affect the interpretation of the message,
    such as TNEF processing, etc.

  * mail.processed
    Called after all internal processing is completed. All Unicode
    processing is complete, bounce detection and other mechanisms have
    completed. This signal is useful to do things like attachment scanning
    or content filtering.
mail: Add useful error log on failed mail processing
logging: Add signal for log handling
Update class.mailparse.php function splitHeaders

function splitHeaders updated in order to correctly parse mail header lines
starting with tabs
Merge remote branch 'upstream/develop-next' into develop-next