Refer to MS-DOS using the same name everywhere.

Refer to MS-DOS using the same name everywhere.

* admin/FOR-RELEASE: ``MS-DOG'', ``MSDOG'' and ``msdog'' become
``MS-DOS''; ``msdog'' in filenames becomes ``msdos''.
* admin/MAINTAINERS: ditto.
* doc/emacs/Makefile.in (EMACSSOURCES): ditto.
* doc/emacs/emacs-xtra.texi: ditto.
* doc/emacs/emacs.texi: ditto.
* doc/emacs/makefile.w32-in: ditto.
* doc/emacs/msdog-xtra.texi: ditto, and rename file.
* doc/emacs/msdog.texi: ditto, and rename file.
* lisp/arc-mode.el: ditto.
* lisp/frame.el: ditto.