[plt-scheme] backups and hiding code in 299.100

Two quick questions:

1) 299.100 seems to make backup files: when I edit blat.ss, blat.ss~ is 
created. Is there any way to turn this behaviour off? I couldn't find 
anything in Preferences.

2) Is there a platform-independent way to provide code to someone but 
hide the details? The way I want to use this is to give students a 
working implementation of something I'm asking them to do on an 
assignment so that they can test their functionality against it.

Thanks. --PR