Allow rewriting of a file and extending a file upto the end of the
allocated block on a full filesystem.

From: Chris Mason <mason@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>