A backport of scheme-mode from GNU Emacs 29+

Paul Eggert 6a54bcf4d4 Merge from emacs-24; up to 2012-12-06T01:39:03Z!monnier@iro.umontreal.ca %!s(int64=12) %!d(string=hai) anos
COPYING f42a75b8d8 Restore files that I seem to have mistakenly deleted. %!s(int64=14) %!d(string=hai) anos
scheme.el ece6eca08a Merge from emacs-24; up to 2012-12-06T01:39:03Z!monnier@iro.umontreal.ca %!s(int64=12) %!d(string=hai) anos