Fix for bug 84714 and bug 88797: You can now change bug groups from the "change several bugs" form even if the bugs aren't all in the same groups.  Also, the groups are no longer cleared when you make a change from the "change several bugs" form (unless you tell it to)
Patch by Joe Robins <jmrobins@tgix.com> and Dave Miller <justdave@syndicomm.com>
r= zach@zachlipton.com
a= justdave@syndicomm.com