[plt-scheme] How to use "planet" portably (i.e., on both v209 and v310)?

In version 209, 
                
                (require (planet "htmlprag.ss" ("neil" "htmlprag.plt" 2 0)))

works.  But it doesn't work in 301 (I get 

        planet: Could not find package matching ("htmlprag.plt" 2 (0 #f) ("neil")) in: (planet "htmlprag.ss" ("neil" "htmlprag.plt" 2 0))

); but (planet "htmlprag.ss" ("neil" "htmlprag.plt" 1 2)) _does_ work
in 301, and doesn't work on 209 (I get "Could not find matching
package").  How can I require that package in a way that works on
both?
-- 
I think that novels that leave out technology misrepresent
life as badly as Victorians misrepresented life by leaving out
sex.
        -- Kurt Vonnegut, Jr.