This patch changes the behavior of the mailer to support a 'text' option to
hint if the message is a text-only message. If so, no HTML processing will
be performed on the message and a text-only email (with no inline
attachments) will be emitted and sent.

Also converts ROOT_DIR detection to always use forward slashes. And it fixes
the removal of the leading double-backslash on Windows UNC names (fixes #649)

The previous implementation did not work correctly for symlinked folders.
The new approach uses debug_backtrace() and ROOT_DIR to determine the
difference between ROOT_DIR and the osTicket installation path.

This thing is like a turd that won't flush

Also, allow for the administrator to manually define the ROOT_PATH in the
config file (the very last mile).

Anything that would happen after the last patch was applied would never be
logged, because the system would immediately indicate that no upgrade was
pending.

This patch allows the upgrader to upgrade multiple database update
'streams'. The main stream is renamed to 'core' to reflect changes made
to the config class. This will significantly ease customizations
requiring database customizations, and will make plugins requiring
database changes possible.

- timezone_offset was dropped from the config table at 1.7-dpr1
- upgrader: only apply five patches in one request
- upgrader: fix readPatchInfo to work correctly
- session: support migrating from 1.6 (again)
- config: support migrating from 1.6 (fallback)
- config: no default for 'isonline' setting
- config: fix SQL whitespace issue for schema signature fallbacks
- config: hash 1.6 versions in the schema signature lookup
- upgrader: fix logging bug in attachment migration

Allow (a subset of) the configuration to also be saved in the session to
make session-backed data more consistent and compatible with up-and-coming
multi-site setups.

Change the config table from a column-based table to a key-value table
with namespacing. This allows several parts of osTicket to store their
respective configurations in the same table without requiring database
structure updates

'namespace' is reserved in PHP

 - get_path_info() - simply returns the PATH_INFO if available
 - get_var() - get var from an array - checks if index is set & can validate type.

Change /api/task/* -> /api/tasks/*

Add routine to import emailed & api files

* Append page url to error alerts - useful in determining which page triggered the error.

Move pending upgrade check to core class from config. Decouple core from config (doesn't extend config anymore)