Adapt to the changes in vc-hooks.el, namely, the new

Adapt to the changes in vc-hooks.el, namely, the new
'none-value of vc-locking-user, and the consistent caching
of all properties.  Especially, make the properties survive
check-ins and check-outs.  Various minor bug fixes.

(vc-file-clear-masterprops): New function.

(vc-backend-checkin, vc-backend-revert): Set vc-locking-user
to 'none if the file is unlocked.

(vc-backend-checkin, vc-backend-revert, vc-backend-checkout):
Use vc-file-clear-masterprops, and adjust those properties
that are not cleared.

(vc-resynch-window):  Temporarily remove vc-find-file-hook, so
that we don't lose the file properties during check-in/out.

(vc-resynch-window): Do not try to delete the current window if
`vc-keep-workfiles' is nil (doesn't make sense; killing the
buffer is enough.)

(vc-backend-checkin): Rewrote the code that adjusts the default
branch and removes any locks that might remain after check-in.

(vc-cancel-version): Abort with error message in the CVS case.
(The error used to be signalled in vc-backend-uncheck, which is
a little too late.)

(vc-minor-revision): Function removed.