Patched CCO.Diag

  Since we want to reuse the Diag datatypes defined in
  src/CCO/Diag/AG/Base.ag we need to include it in
  Type/AG.ag. However we need also to import CCO.Diag
  for importing the Diag type and constructors.
  Since include inlines the content of the file we end up
  with a duplicate instance Tree for Diag and Diag_.
  In order to avoid this such instance has been moved from
  src/CCO/Diag/AG/Base.ag to src/CCO/Diag/Base.hs.

  Temporarily the original Makefile has been readded:
  Using only cabal seems not to work correctly.