OF-616: Group names are cached in two manners: one time in a collection that contains all group names, but also for paginated requests. Upon changing the cache, those paginated cached collections should also be tossed.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@13493 b35dd754-fafc-0310-a699-88a17e54d16e