commit 557ea5dd upstream.

It's no doubt the comprehensive tree block checker will become larger,
so moving them into their own files is quite reasonable.
Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
[ wording adjustments ]
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 4.4:
 - The moved code is slightly different
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>