patch applied (cabal): Preprocessor output never gets written back to the source dir.

[Ian Lynagh]

Tue Jul 17 10:40:26 PDT 2007  Thomas Schilling <nominolo at gmail.com>
  * Preprocessor output never gets written back to the source dir.
  
  'preprocessSources' now gets an additional flag to determine whether
  to process all sources (for building) or only platform independent
  ones (for sdist).

    M ./Distribution/PreProcess.hs -25 +26
    M ./Distribution/Simple.hs -2 +2
    M ./Distribution/Simple/Build.hs -1 +1