----- Change Log
1.4
 * Added MyBB 1.8 compatibility.
 * Fixed bug in file check.
 * Re-worded one the description of the groups field.

1.3
 * It is now possible to choose a field name and a respective value (instead of the previous default 'action' field).
 * Permission rules are now sorted by filename (ascending order).
 * Empty field name now means that all field names are affected - similar to a wildcard.
 * Fixed a few language typos.
 * Permission rules are now cached saving one query per page.

1.2
 * Guests group was not being shown in the list.

1.1
 * Changed license to GPLv3.
 * Compatible with MyBB 1.6 only.
 * Now shows a list of user groups instead of asking for the group ID's.