fix ext3 block bitmap leakage

This patch fixes ext3 block bitmap leakage,
which leads to the following fsck messages on
_healthy_ filesystem:
Block bitmap differences:  -64159 -73707

All kernels up to 2.6.17 have this bug.

Found by
   Vasily Averin <vvs@sw.ru> and Andrey Savochkin <saw@sawoct.com>
Test case triggered the issue was created by
   Dmitry Monakhov <dmonakhov@sw.ru>

Signed-Off-By: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>