Remove Language.Hi in favour of using the ghc-api directly, fix to work with GHC 6.8.2.

This is still *very* kludgey, and it needs lots of work which I'm not
entirely prepared for, seeing as I really don't know anything about
the ghc-api and how things are supposed to fit together. It is quite
conceivable that the code could be simplified much further by someone who
actually understands the ghc-api, and there may be bugs related to the fact
that I don't actually know what some things do. However, this builds
and does appear to work. Most of the testsuite is passing.

testsuite/eval/eval_/Main.hs

@@ -2,7 +2,7 @@
 import System.Eval.Haskell
 
 main = do i <- eval_ "Just (7 :: Int)" 
-                     ["Maybe"] 
+                     ["Data.Maybe"] 
                      ["-fglasgow-exts"] 
                      []
                      [] :: IO (Either [String] (Maybe (Maybe Int)))