darcs patch: Cabal API and test suite changes

Hi all, This patch introduces a Cabal type which is used a Monad/State used to carry along the logger functions and the verbosity. With this you can now override the logging/error functions used in Cabal. This allows IDEs to identify individual messages. You also no longer need to pass along the verbosity argument. Distribution.Api.Cabal contains the core of this patch. Please do not apply this patch until the one for cabal-install has been submitted. It passes all the tests and compiles with no warnings. Regards, Tamar