Some improvements in vc

Some improvements in vc

* lisp/vc/vc-hooks.el (vc-state, vc-working-revision):
Check, whether FILE is registered.

* lisp/vc/vc-rcs.el (vc-rcs-checkout-model): Return `locking'
for nonexistent files.

* test/lisp/vc/vc-tests.el (w32-application-type): Declare.
(vc-test--revision-granularity-function)
(vc-test--unregister-function): Use `vc-call-backend'.
(vc-test--run-maybe-unsupported-function): New defmacro.
(vc-test--register, vc-test--state, vc-test--working-revision)
(vc-test--checkout-model): Use it.  Fix also expected results.
(vc-test-src02-state, vc-test-rcs04-checkout-model): They pass now.