(vc-do-command): Arrange for the default-directory variable

(vc-do-command): Arrange for the default-directory variable
in *vc* to be re-set each time this function uses it.
Discard current dir from front of FILE later on,
and only if last = `WORKFILE'.

Undo Dec 10 change:
(vc-directory, vc-dired-reformat-line): Changed back.
(vc-directory-18): Old function restored.
(vc-dir-all-files): Function deleted.

(vc-next-action-on-file): If file is not registered,
check file out after registering it.
(vc-next-action-dired): Restore the window configuration after
doing vc-next-action on each file in a VC-dired buffer.
(file-regular-p-18): New function.
(file-regular-p): Define, if not already defined.