Make `checkout-model' apply to filesets.

Make `checkout-model' apply to filesets.
* vc-hooks.el (vc-checkout-model): Rewrite.
(vc-before-save, vc-after-save): Adjust callers accordingly.
* vc.el (vc-editable-p, vc-next-action, vc-checkout, vc-update)
(vc-transfer-file): Adjust callers accordingly.
* vc-rcs.el (vc-rcs-checkout-model): Adjust arg.
(vc-rcs-state, vc-rcs-state-heuristic, vc-rcs-receive-file)
(vc-rcs-checkout, vc-rcs-fetch-master-state): Use vc-rcs-checkout-model
instead of vc-checkout-model.
* vc-mcvs.el (vc-mcvs-revert):
Use vc-mcvs-checkout-model i.s.o vc-checkout-model.
* vc-cvs.el (vc-cvs-checkout-model): Adjust arg.
(vc-cvs-revert): Use vc-cvs-checkout-model i.s.o vc-checkout-model.
* vc-svn.el (vc-svn-checkout-model):
* vc-hg.el (vc-hg-checkout-model):
* vc-git.el (vc-git-checkout-model):
* vc-bzr.el (vc-bzr-checkout-model): Adjust arg.