bug#23414: 24.5; Scheme-Mode: missing UNLESS and WHEN from R7RS

[Peter]

M-x scheme-mode is missing WHEN and UNLESS from R7RS for highlighting
and correct indentation.

I suggest adding the following two lines to fix indentation:

    (put 'when 'scheme-indent-function 1)
    (put 'unless 'scheme-indent-function 1)

Around line 537 in progmodes/scheme.el.gz would probably be good.

To get fontification correct, "when" and "unless" should be added to
scheme-font-lock-keywords-2, probably to the list around line 302 in
progmodes/scheme.el.gz.

Thank you for any help with this!

Greetings, Peter