Re-ordered the sequence of checking email addresses against valid system

Re-ordered the sequence of checking email addresses against valid system
addresses. This allows us to have a GAB entry for rooms and allows
messages originating internally to be addressed to a room.
For the GAB lookup to work as expected the email address for the room
must be simply room_roomname without the @domain. If the domain part is
included the aliasing routines will translate it into the address of the
person who created the GAB entry.
This should fix bug #324.