Send group notices through the same messaging module mechanism used to send group chat to avoid timeout issues when sending messages to large groups.

Only implementing for XmlRpcGroups initially to test.
May require MessageOnlineUsersOnly = true in [Groups] to be effective.
In relation to http://opensimulator.org/mantis/view.php?id=7037
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim