GCalc updates.

* Lots of racket-isms.

* Add ".rktd" to the sample file.

* Fix an old bug where the large display wouldn't get refreshed.
Fix renamed file in props.
Style changes.

No need to stick with the srfi-1 style of `lis' and `recur'.  I also
removed the srfi-1 comment since this code is straightforward.  (I keep
such comments if there's something non-trivial that was taken.)