Fixup missing column in upgrades from < v1.8.0

There was a major goof for osTicket 1.8.0 where the installer created a
`form_id` column in the `%filter` table; however, the upgrader neglected to
add the column. Therefore, users who have upgraded from a version previous
to 1.8.0 will not have the `form_id` column in their database whereas users
who installed osTicket >= v1.8.0 and upgraded will have the column. Since
MySQL has no concept of `ADD IF NOT EXISTS`, this dynamic query will
assist with adding the column if it doesn't exist.

Thanks, http://stackoverflow.com/a/16405301/1025836