* log-view.el (log-view-diff-changeset): New function.

* log-view.el (log-view-diff-changeset): New function.
(log-view-mode-map, log-view-mode-menu): Bind it.
(log-view-per-file-logs, log-view-vc-fileset)
(log-view-vc-backend): New variables.
(log-view-find-revision, log-view-modify-change-comment)
(log-view-annotate-version): Throw an error if the log is for more
than one file and we can't find the current file.  Get the current
file from log-view-vc-fileset if necessary.
(log-view-diff): Get the current file from log-view-vc-fileset if
necessary.

* vc.el (vc-print-log): Set log-view-vc-fileset and log-view-vc-backend.

* vc-hg.el (vc-hg-log-view-mode): Call the log method only once.
(vc-hg-log-view-mode): Declare for compiler.
(vc-hg-log-view-mode): Set log-view-per-file-logs and
log-view-file-re.
(vc-hg-diff): If no file is passed, use default-directory for cwd.

* vc-bzr.el (vc-bzr-log-view-mode): Set log-view-per-file-logs.

* vc-svn.el (vc-svn-log-view-mode): New derived mode.