There were two problems here:
1) On object group update, we looked for the group is the IClientAPI group cache rather than in the groups service. This fails to groups created newly in that session
2) On object group update, we weren't setting the HasGroupChanged flag. This meant that the change was not persisted unless some other action set this flag.
This commit fixes these issues and hopefully addresses http://opensimulator.org/mantis/view.php?id=5588
This commit also moves HandleObjectGroupUpdate() to the GroupsModule from the Scene.PacketHandlers.cs file
* Simplified the interest management code to make it easier to add new policies. Prioritization and reprioritization share code paths now
* Improved the distance and front back policies to always give your avatar the highest priority
Justin Clark-Casey (justincc)