Fix separation into full and RTS-only ways, add comments.
Fix separation into full and RTS-only ways, add comments.

snowleopard/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,snowleopard/hadrian,izgzhen/hadrian,sdiehl/ghc,sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc