Description
Not our "we build with this version of GHC" window, but the "Cabal knows how to drive this version of GHC" window. Based on #3034, we claim to support GHCs all the way back to 6.4.2. When, if ever, do we drop support? Is this claim even meaningful, given we don't actually test these GHCs?
Once we define a support window, we should start testing these versions on Travis. This is a bit delicate, we need to install both the old GHC and the new GHC. Fortunately, hvr's PPA installs each version of GHC to a separate folder, which is great; even better, builds for precise go all the way back to 6.12 (perhaps that should be our actual support window?) Another thing that needs to be dealt with is being able to run the tests using a --with-ghc which is not the same as the version of Cabal that was built.