(vc-simple-command): New function.

(vc-simple-command): New function.
(vc-fetch-master-properties): CVS case: Use it.
(vc-lock-from-permissions, vc-file-owner, vc-rcs-lock-from-diff):
New functions.
(vc-locking-user): Largely rewritten.  Uses the above, handles RCS
non-strict locking.  Under CVS in CVSREAD-mode, learn the locking state
from the permissions.
(vc-find-cvs-master): Use vc-insert-file, rather than
find-file-noselect. Greatly speeds up things.
(vc-consult-rcs-headers): Bug fix, return status in all cases.