patch applied (cabal): Record if pre-processors are platform independent

[Duncan Coutts]

Tue May  1 07:21:47 PDT 2007  Duncan Coutts <duncan.coutts at worc.ox.ac.uk>
  * Record if pre-processors are platform independent
  PreProcessor is now a record with a couple fields.
  Quite a few knock-on changes due to changing this data type.

    M ./Distribution/PreProcess.hs -60 +104
    M ./Distribution/Simple.hs -3 +6
    M ./Distribution/Simple/Hugs.hs -2 +2