MFC r197445:

MFC r197445:
Let fall down in the hard path (thus handling shared waiters wakeup
correctly) for the shared waiters also in the rwlock held in shared mode
as well, fixing possible deadlocks.

Please note that this is a special condition as we want this fix in
before RC2 as we assume it is critical and so it has been handled
as an instant-merge.  For the STABLE_7 branch, 1 week before the MFC
is assumed.

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@197452 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f