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.