- 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.

Drop required usage of MyISAM tables, and drop fulltext indexes as they
are not used in the code currently anyway. Also, use a blob to store
session data so as not to waste space with UTF-8 encoding. Lastly, fix
session_id storage to use VARCHAR(255) which is required for versions
of MySQL < 5.0.3, and use ascii for the storage model for the
session_id as it will contain simple characters only.

Migrate the PHP session from disk to database live. To pull this off, the
session contents are written to database under the current session id. When
the `ostversion` column is dropped from the %config table, the system will
automatically switch to database-backed sessions in osTicket 1.7 mode.

This is sort-of hacked together by carefully calling a instance method of
the osTicketSession class statically, and modify the instance method to
support static invocation.