Windows: split cm_buf_t.flags field to ensure proper locking

Windows: split cm_buf_t.flags field to ensure proper locking

It turns out that for all these years the locks protecting
the cm_buf_t flags field have been racy.  Some of the flags
were protected by the cm_buf_t mutex and others by the
buf_globalLock.  This patchset splits the flags field so that
the appropriate lock will be used exclusively to protect a
common set of flags.

LICENSE MIT

Change-Id: I85c98c85244c987df30a811d405f7d897e407ba2
Reviewed-on: http://gerrit.openafs.org/1759
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>