s3-privileges: add handling of both old and new formats in database

s3-privileges: add handling of both old and new formats in database

We update privileges on a per-record basis instead of all at once, as
this maintains maximum compatibility is someone uses old tools with a
new version of Samba. The also auto-detects the byte order of the old
entries in the database, and copes with either native or reversed byte
order.

Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>