ext2: don't inherit inappropriate inode flags from parent

At present BTREE/INDEX is the only flag that new ext2 inodes do NOT
inherit from their parent.  In addition prevent the flags DIRTY, ECOMPR,
INDEX, IMAGIC and TOPDIR from being inherited.  List inheritable flags
explicitly to prevent future flags from accidentally being inherited.

This fixes the TOPDIR flag inheritance bug reported at
http://bugzilla.kernel.org/show_bug.cgi?id=9866.

Signed-off-by: Duane Griffin <duaneg@dghda.com>
Acked-by: Andreas Dilger <adilger@sun.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>