Patch to optimize for large installations (>5000 users >20000 groups) where...

Patch to optimize for large installations (>5000 users >20000 groups) where subadmins have access to many of groups (>250)
- UsersController:editUser() calls isUserAccessible() even if the user is admin

This fix reduces API calls to editUser (ex change locale/display name) from >2 minutes (!) to ~3 seconds per call in average.

Signed-off-by: Mikael Hammarin <mikael@try2.se>