We need to be careful differentiating between a resync of a complete array,
in which we can clear the bitmap, and a resync of a degraded array, in
which we cannot.

This patch cleans all that up.

Cc: Paul Clements <paul.clements@steeleye.com>
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>