Windows: cm_BufWrite() must wait in cm_SyncOp()

Windows: cm_BufWrite() must wait in cm_SyncOp()

Now that it is permissible for more than one store data operation
to construct BIOD lists in parallel, cm_BufWrite() must be willing
to wait in cm_SyncOp().  Otherwise, the daemon threads will spin.

Reviewed-on: http://gerrit.openafs.org/6423
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 17ce77f843e01ff96f66e05b4b932b0c6187493e)

Change-Id: I8ae9d057413252e73774c5209465223fa5a36947
Reviewed-on: http://gerrit.openafs.org/6818
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>