idmap_hash: Add the idmap/nss-info provider from Likewise Open.
* Port the Likewise Open idmap/nss_info provider (renamed to
idmap_hash).
* uids & gids are generated based on a hashing algorithm that collapse
the Domain SID to a 31 bit number. The reverse mapping from the
high order 11 bits to the originat8ing sdomain SID is stored in
a has table initialized at start up.
* Includes support for "idmap_hash:name_map = <filename>" for the
name aliasing layer. The name map file consist of entries in
the form "alias = DOMAIN\name"