Fix version installs with justhub repo

If we specify a version of the package in the justhub repo, we need to make sure
we specify the same version for both the haskell meta package and the
haskell-min meta package. Otherwise it will still install the latest version of
ghc. Added tests to ensure the correct ghc version gets installed.
there is no real reason to use <code>%w[]</code>here, the standard way would be to just do <code>["haskell-platform"]</code>