password API needed

[Luke Kenneth Casson Leighton]

ok: i've just added code that allows "optional" support for get/add/mod -
smb_passwd or sam_passwd functions.  there are three get, one add and one
mod set of smb and sam21 functions.

if neither are supported by the back-end password database, a run-time
warning is generated.

i also reverted some code that immediately converts rids to unix uids,
inside the lib/rpc code.  i do not believe that this is a good idea: it
places a restriction on all password database systems that there must
exist a monotonic mapping of unix uids to nt user rids, in order to do
proper lookups by rid (which is unique).

the limitation (restriction) inherent in one password database system,
because it does not support rids and has to use pdb_user_rid_to_uid()
should not be imposed on the samba domains code, in my opinion.

particularly as it's unnecessary and does not affect the unix file-service
side of samba in any way.

luke