Better handling of uid/gid -> RID and RID -> uid/gid code.

Better handling of uid/gid -> RID and RID -> uid/gid code.

All uids and gids must create valid RIDs, becouse other code expects this, and
can't handle the failure case. (ACL code in particular)

Allow admins to adjust the base of the RID algorithm, so avoid clashes with
users brought in from NT (for example).

Put all the algorithm code back in one place, so that this change is global.

Better coping with NULL sid pointers - but it still breaks a lot of stuff.

BONUS: manpage entry for new paramater :-)

counter based rids for normal users in tdbsam is disabled for the timebeing,
idra and I will work out some things here soon I hope.

Andrew Bartlett
(This used to be commit 5275c94cdf0c64f347d4282f47088d084b1a7ea5)