hurd: SCM_CREDS support

hurd: SCM_CREDS support

Svante Signell  <svante.signell@gmail.com>
Samuel Thibault  <samuel.thibault@ens-lyon.org>

	* sysdeps/mach/hurd/sendmsg.c (__libc_sendmsg): On SCM_CREDS
	control messages, record uids, pass a rendez-vous port in the
	control message, and call __auth_user_authenticate_request to
	make auth send credentials on that port.  Do not wait for a
	reply.
	* sysdeps/mach/hurd/recvmsg.c (contains_uid, contains_gid,
	check_auth): New functions.
	(__libc_recvmsg): On SCM_CREDS control messages, call check_auth
	to check the passed credentials thanks to the answer from the
	auth server.
	* hurd/Makefile (user-interfaces): Add auth_request and
	auth_reply.

Gbp-Pq: Topic hurd-i386
Gbp-Pq: Name tg-sendmsg-SCM_CREDS.diff