[plt-scheme] versions of collects and .plt files

Eli Barzilay wrote:

>It should work fine with subcollections too, as long as you don't
>package the `compiled' directory too.  (I don't remember any bugs in
>that are.)
>  
>
There was a bug in which planet packages needed a slightly different 
format for the compile-subcollections info.ss field than non-planet .plt 
files; that was fixed from 300 to 301. But that shouldn't impact people 
who aren't using planet.

-jacob