[plt-scheme] backwards compatibility and planet libraries

The planet docs say that you should bump the major revision whenever you 
break backwards compatibility. Clearly this is right when you remove or 
modify a part of the interface, so that if planet automatically updates 
to a newer minor version, it doesn't suddenly break some other code that 
depends on it.

What about *adding* new functionality? Given that planet often refuses 
to update the minor version, if some code depends on a newer minor 
version because it has new functionality, but planet won't update to the 
newer version, that code will be broken.

Does this mean I should up the major version even when I add 
conservative extensions to the interface?

Dave