[plt-scheme] collection not found: "planet" on Windows ...

Problem solved: I'd foolishly gotten double-quote marks into my PATH
environment variable.  That is, where I should have had it set to
something like 

        PATH=C:\WINNT\system32;C:\Program Files\PLT

I instead had

        PATH=C:\WINNT\system32;"C:\Program Files\PLT"

-- 
There is such a thing as American-ness.  ... [H]ackers ... come
closest of any group I know to embodying it.  Closer, probably, than
the men running our government.
        -- Paul Graham