Add vc-ignore.

Add vc-ignore.

* lisp/vc/vc.el (vc-ignore): New function.

* lisp/vc/vc-svn.el (vc-svn-ignore): New function.

* lisp/vc/vc-hg.el (vc-hg-ignore): New function.

* lisp/vc/vc-git.el (vc-git-ignore): New function.

* lisp/vc/vc-dir.el (vc-dir-mode-map): Add key binding for vc-dir-ignore
(vc-dir-ignore): New function.

* lisp/vc/vc-cvs.el (vc-cvs-ignore): New function.
(cvs-append-to-ignore): Moved from pcvs.el.

* lisp/vc/vc-bzr.el (vc-bzr-ignore): New function.

* lisp/vc/pcvs.el (vc-cvs): Require 'vc-cvs.