Generic Unix Tarball doesn't enforce building against platform versions of libs

[dons]

The unix tarball build process will allow ghc to pick up libs from the environment. This means we can end up building against the wrong versions of libs, should the user already have installed them.

A case:

• network depends on parsec
• user has parsec 3 installed
• platform builds and registers parsec 2
• build fails due to parsec 3 not having profiling (or silently suceeds linked against parsec 3)

Network/URI.hs:108:7:
    Could not find module `Text.ParserCombinators.Parsec':
      Perhaps you haven't installed the profiling libraries for package `parsec-3.0.0'?
      Use -v to see a list of the files searched for.

[refold]

Milestone 2009.4.0 deleted