40_blkdev-pagecache-3

	This moves blkdev in pagecache. It synchronizes the buffercache with
	pagecache if the blkdev is closed and a ro fs was mounted under it.
	It should be safe to use except it obviously breaks the ramdisk driver
	very badly (initrd included) so this has to stay in the experimental directory
	for now (though I run it on my systems and I expect it to be otherwise
	stable). The fix in the ramdisk consists in doing a rewrite of the request
	function to lookup on the pagecache instead of the buffercache and I
	didn't had the time to do it yet. If there's any volunteer to fix
	ramdisk let me know so we don't duplcate efforts.