[PATCH] md: make sure md bitmap is cleared on a clean start.

As the array-wide clean bit (in the superblock) is set more agressively than
the bits in the bitmap are cleared, it is possible to have an array which is
clean despite there being bits set in the bitmap.

These bits will currently never get cleared, as they can only be cleared by a
resync pass, which never happens.

No, when reading bits from disk, be aware of whether the whole array is known
to be in sync, and act accordingly.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>