added a boolean to the group mapping functions to specify if we need or

added a boolean to the group mapping functions to specify if we need or
not the privileges. Usually we don't need them, so the memory is free
early.

lib/util_sid.c: added some helper functions to check an SID.

passdb/passdb.c: renamed local_lookup_rid() to local_lookup_sid() and pass
an RID all the way. If the group doesn't exist on the domain SID,
don't return a faked one as it can collide with a builtin one. Some rpc
structures have been badly designed, they return only rids and force the
client to do subsequent lsa_lookup_sid() on the domain sid and the builtin
sid !

rpc_server/srv_util.c: wrote a new version of get_domain_user_groups().
Only the samr code uses it atm. It uses the group mapping code instead of
a bloody hard coded crap. The netlogon code will use it too, but I have to
do some test first.

	J.F.
(This used to be commit 6c87e96149101995b7d049657d5c26eefef37d8c)