* vc.el: Rename VC methods that were missed when vc-status was

* vc.el: Rename VC methods that were missed when vc-status was
renamed to vc-dir.
* vc-svn.el (vc-svn-dir-extra-headers): Rename from
vc-svn-status-extra-headers.
* vc-hg.el (vc-hg-dir-printer): Rename from vc-hg-status-printer.
(vc-hg-dir-extra-header): Rename from vc-hg-status-extra-headers.
* vc-git.el (vc-git-dir-printer): Rename from vc-dir-status-printer.
(vc-git-dir-extra-headers): Rename from vc-git-status-extra-headers.
* vc-dir.el (vc-dir-mode): Use vc-dir-printer instead of
vc-dir-status-printer.
(vc-dir-headers): Use `dir-extra-headers' instead of
`status-extra-headers'
(vc-dir-printer): Rename from vc-dir-status-printer.
(vc-default-dir-extra-headers): Rename from
vc-default-status-extra-headers.
* vc-cvs.el (vc-cvs-dir-extra-headers): Rename from
vc-cvs-status-extra-headers.