This patch makes the possessor permissions on a key additive with
user/group/other permissions on the same key.

This permits extra rights to be granted to the possessor of a key without
taking away any rights conferred by them owning the key or having common group
membership.
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>