Reinstate test for getDotCabal or remove feature

[mgsloan]

Currently, the test with withIncludes and TargetsExclude fails because the cabal file generated by getDotCabal doesn't have any dependency constraints.

This is pretty bizarre, because when I add some debugging of the computed deps, here, they look correct. So the only thing I can think of is a change in behavior for showGenericPackageDescription, part of the Cabal library.