Windows: AFSVolSync creationDate based readonly volume versioning

Windows: AFSVolSync creationDate based readonly volume versioning

Implement readonly volume versioning based upon the .readonly
volume creation date as reported in the AFSVolSync output
parameter of every RXAFS RPC.

Whenever a new callback is obtained for an object stored within
a .readonly volume, the volume creation date is recorded in the
cm_volume object along with the callback expiration time and
a reference to the server that issued it.  These values are
used to determine if a callback is present when the cm_scache
object's volume creation date matches the cm_volume object's
volume creation date.  If there is no match, the cm_scache
object's individual callback information is used to determine
whether a callback has been registered.

This mechansism ensures that the whole-volume callback issued
in response to a RXAFS_FetchStatus request against a .readonly
volume can be applied to all objects that are cached from the
same version of the .readonly volume instance.

LICENSE MIT

Reviewed-on: http://gerrit.openafs.org/654
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Asanka Herath <asanka@secure-endpoints.com>
Tested-by: Asanka Herath <asanka@secure-endpoints.com>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>