Add tty locking around the audit and accounting code.

The whole current->signal-> locking is all deeply strange but it's for
someone else to sort out.  Add rather than replace the lock for acct.c
Signed-off-by: NAlan Cox <alan@redhat.com>
Acked-by: NArjan van de Ven <arjan@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>