Fix a bug in udf where it would write uid/gid = 0 to the disk for files
owned by the id given with the uid=/gid= mount options.  It also adds 4 new
mount options: uid/gid=forget and uid/gid=ignore.  Without any options the
id in core and on disk always match.  Giving uid/gid=nnn specifies a
default ID to be used in core when the on disk ID is -1.  uid/gid=ignore
forces the in core ID to allways be used no matter what the on disk ID is.
uid/gid=forget forces the on disk ID to always be written out as -1.

The use of these options allows you to override ownerships on a disk or
disable ownwership information from being written, allowing the media to be
used portably between different computers and possibly different users
without permissions issues that would require root to correct.

Signed-off-by: Phillip Susi <psusi@cfl.rr.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>