[racket] Liitin screencast tutorial

Sorry, absolutely nothing personal (cosi fan tutti)

- It works/exists today (Racket 5.1)
- It it very likely to work/exist tomorror, as well. (PLT 4.25)
- It will propably work/exist day after (PLT 4.0)
- On third day it's 50:50 (PLT 300)
- after fifth day you are better off reading from frog's guts (pre PLT 100)

It took just one standard change to force me to go through all existing
code.

IF (ELSE clauses R5RS>R6RS)

On the user level, the validity of the program didn't change in any way.

br, jukka