patch applied (cabal): Add a "build-tools:" field to the cabal file format

[Duncan Coutts]

Thu Aug 23 14:29:46 PDT 2007  Duncan Coutts <duncan at haskell.org>
  * Add a "build-tools:" field to the cabal file format
  It's the same format as the build-depends, eg:
  build-tools: cpphs, c2hs >= 0.15
  During the configure step we try to configure the listed programs and
  if a version range is specified then we check that it is satisfied.

    M ./Distribution/PackageDescription.hs +6
    M ./Distribution/Program.hs +5
    M ./Distribution/Simple/Configure.hs -4 +22