Change `dir-status' to not take (and pass) status-buffer.

Change `dir-status' to not take (and pass) status-buffer.
(vc-status-create-fileinfo): Make `extra' optional.
(vc-status-busy): New fun.
(vc-status-menu-map): Use it.
(vc-status-crt-marked): Remove.
(vc-status-update): Rename from vc-status-add-entries.
Add argument so as to prevent addition of entries.  Rewrite.
(vc-update-vc-status-buffer): Remove.
(vc-status-refresh): Don't remove old entries, set them to
up-to-date instead.  Also do it after the update is complete.
(vc-status-marked-files): η-reduce.