[PATCH] list: introduce list_replace() helper

list_replace() is similar to list_replace_rcu(), but unlike
list_replace_rcu() it

	could be used when list_empty(old) == 1

	doesn't use barriers

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>