(log-view-mode-map): Unsatisfying fix for when cvs-mode-map is not
available.
(log-view-font-lock-keywords): Only use cvs-filename-face if present.
(log-view-current-file): Only use cvs-pcl-cvs-dirchange-re if present.
log-view-*-(message|file) and use easy-mmode-define-navigation.
(log-view-message-re): Match SCCS format as well.
And match the revision line rather than the dashed separator line.
(log-view-mode): Use the new define-derived-mode.
(log-view-current-tag): Fill in with an actual implementation.
