One can do "chattr +j" on a file to change its journalling mode.  Fix
writeback mode with "nobh" handling for it.

Even though, we mount ext3 filesystem in writeback mode with "nobh" option,
some one can do "chattr +j" on a single file to force it to do journalled
mode.  In order to do journaling, ext3_block_truncate_page() need to
fallback to default case of creating buffers and adding them to transaction
etc.
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>