* vc.el (vc-editable-p): Minor optimization.

* vc.el (vc-editable-p): Minor optimization.
(edit-vc-file, vc-next-action-on-file): Don't use find-file.
(vc-find-new-backend): New function split from vc-responsible-backend.
(vc-register): Use it.
(vc-responsible-backend): Remove REGISTER arg and add BACKENDS arg.
(vc-unregister): Drop BACKEND arg (it doesn't work anyway).
(vc-default-unregister, vc-revert-buffer): Docstring fix.
(vc-clear-headers): Don't use find-file.
(vc-revert-buffer): Use `and' again (must have been a braino).
(vc-switch-backend): Only prompt if requested.
(vc-default-receive-file): Update call to vc-unregister.

* vc-rcs.el (vc-rcs-unregister): Keep a backup of the master file.
(vc-rcs-receive-file): Avoid with-vc-properties.
Update call to vc-unregister.
Use constant `RCS' rather than (dynamically bound) var `backend'.