[PATCH] ocfs2: Remove expensive bitmap scanning

Enable expensive bitmap scanning only if DEBUG option is enabled.
The bitmap scanning quite loads the CPU and on my machine the write
throughput of dd if=/dev/zero of=/ocfs2/file bs=1M count=500 conv=sync
improves from 37 MB/s to 45.4 MB/s in local mode...

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>