Reduce the number of versioned files storing the short copyright string

Reduce the number of versioned files storing the short copyright string

* configure.ac (copyright): New output variable.
(COPYRIGHT): New AC_DEFINE.

* admin/admin.el (set-copyright): No more need to set copyrights for
nextstep, or .c files.  Add configure.ac and config.nt.

* lib-src/ebrowse.c (version):
* lib-src/etags.c (print_version): Use COPYRIGHT.

* nextstep/templates/Info-gnustep.plist.in:
* nextstep/templates/InfoPlist.strings.in:
* nextstep/templates/Info.plist.in: Let configure set copyright.

* nt/config.nt (COPYRIGHT): New.

* src/emacs.c: Use COPYRIGHT.