patch applied (cabal): Put pre-processed source into the dist/build dir rather than src dirs

[Duncan Coutts]

Sun Apr 22 02:56:31 PDT 2007  Duncan Coutts <duncan.coutts at worc.ox.ac.uk>
  * Put pre-processed source into the dist/build dir rather than src dirs
  This is generally just a nicer thing to do, we should probably aim to
  not write any files into the source tree at all.
  The main change is in the preprocessModule function. It now takes an extra
  arg which is the destination directory. For now I'm passing the buildDir,
  but we could consider putting pre-processed files into a separate fir
  from where the .o and .hi files end up.
  To work out the correct destination file we need to know not only the source
  file but which of the search dirs it was found in, since the relative file
  name will be the name of the source file relative to the search dir it was
  found in, not the name relative to the top of the source tree. This is so that
  we will be able to find the pre-processed .hs file just by adding dist/build
  to the sources search path when we compile (eg with -i for ghc).
  This almost certainly breaks the sdist thing where pre-processed files get
  included into the tarball. So that'll need looking at.

    M ./Distribution/PreProcess.hs -14 +28
    M ./Distribution/Simple/GHC.hs -1 +2
    M ./Distribution/Simple/Utils.hs +1