Fix 1320 Multi Region Bug With Group IM's

When a sim has more than one region, group IM's are sent multiple times.
This fix prevents sending received IMs to child agents.

http://mantis.aurora-sim.org/view.php?id=1320
Merge pull request #165 from AliciaRaven/FixGrpChatEcho

Fix Bug 1320 Multi Region Bug With Group IM's