windows cm_BeginDirOp add flags (nobuildtree)

windows  cm_BeginDirOp add flags (nobuildtree)

Add a flags argument to cm_BeginDirOp, and define a flag
CM_DIROP_FLAG_NOBUILDTREE which asserts that the operation
being synchronized does not require scp->dirPlus to be
constructed.

Change-Id: Ibc4345574da3c1e7717c83b64a83260f70a3b06c
Reviewed-on: http://gerrit.openafs.org/2053
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Asanka Herath <asanka@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@openafs.org>