Forward port of a change which Ted made to 2.4's ext2.

HTREE backwards compatibility patch.

"I thought (and assumed) this patch had been applied to both the ext2 and
 ext3 filesystems in the 2.4 kernel.  It turns out it had only made it into
 the ext3 filesystem code.  This means that if an HTREE-enabled filesystem is
 mounted using ext2, it will corrupt the filesystem as far as e2fsck and an
 ext3 htree-enabled kernel is concerned.  (The corruption won't cause any
 data loss, but it will cause e2fsck and an ext3-htree kernel to omit a lot
 of warning messages.)"