Moved around some data in Mercs to help prevent another crash... dunno if it actually will fix it but it can't hurt >_<
Made Merc::AddMercToGroup handle cleaning up old groups as opposed to doing it in each location before AddMercToGroup. This should fix cases where the Merc's owner is invalid and being referenced, which causes the crash located in:

http://www.eqemulator.org/forums/showthread.php?t=36670&page=2
Merge pull request #42 from SecretsOTheP/master

Potential fix for a Merc deconstructor crash.