(vc-fetch-master-properties): Recognize cvs status "Unresolved Conflict".

(vc-fetch-master-properties): Recognize cvs status "Unresolved Conflict".
(vc-locking-user): Count cvs status `unresolved-conflict' as "locked".
(vc-checkout-model): New property and access function (still simplistic).
(vc-after-save-hook): New function.
(vc-mode-line): When the file is locked by somebody else, make the
buffer read-only.  (Formerly this was only done for root.)  Don't
write-protect the buffer if the file is unlocked.  Instead, install
vc-after-save-hook, which "locks" the file when modifications are
saved.