DEVEL15-windows-scache-mx-to-rw-20080302

DEVEL15-windows-scache-mx-to-rw-20080302

LICENSE MIT

Replace the cm_scache_t mutex with a rwlock permitting a small amount
of additional parallelization in places where it is safe to use read
locks instead of write locks.  All functions that eventually call
cm_SyncOp must use write locks.

(cherry picked from commit 69f9b46e69bb7c8c9356b062a8f4908fe38ad14b)