In GridUserService, if a UUID is given consistently use the longest matched entry (as already done by GetGridUserInfo()) in order to avoid problems with multiple entries.

This is to avoid issues where LoggedIn, SetHome, etc were always using the exact UUID match but GetGridUserInfo() would use the longest.
Looks to address http://opensimulator.org/mantis/view.php?id=6986
Merge branch 'justincc-master'