* CacheCork: an error Grant still says 'toT' even though it is transient
Grants with errors must be handled by a client as though no actual
permissions were obtained, so that two clients do not both end up believing
that they own a block which is only temporarily offline. However, the
Grant MESSAGE should still match the request; ie. if you did Acquire.NtoT,
the response must be Grant.toT, even though the 'error' bit signals that
the Grant actually grants no permissions.
This keeps the implementation of request-response tracking in interstitial
adapters and FSMs simple, consistent with the way multibeat errors must
include all their beats.
* Error: handle permissions properly