Make vc-annotate work through copies and renames.

Make vc-annotate work through copies and renames.
* vc-annotate.el (vc-annotate-extract-revision-at-line): Return
the file name too.
(vc-annotate-revision-at-line)
(vc-annotate-find-revision-at-line)
(vc-annotate-revision-previous-to-line)
(vc-annotate-show-log-revision-at-line): Update to get the file
name from vc-annotate-extract-revision-at-line.
(vc-annotate-show-diff-revision-at-line-internal): Change the
argument to mean whether to show a file diff or not.  Get the file
name from vc-annotate-extract-revision-at-line.
(vc-annotate-show-diff-revision-at-line): Update
vc-annotate-show-diff-revision-at-line call.
(vc-annotate-warp-revision): Add an optional file argument.

* vc-git.el (vc-git-annotate-command): Pass -C -C to the blame command.
(vc-git-annotate-extract-revision-at-line): Also return the file
name if found.

* vc-hg.el (vc-hg-annotate-command): Pass --follow to the annotate
command.  Remove unused code.
(vc-hg-annotate-re): Update to match --follow output.
(vc-hg-annotate-extract-revision-at-line): Also return the file
name if found.

* vc.el: Update annotate-extract-revision-at-line documentation.