More hacking on the GHC API to get it into shape for VS

 - load now takes a LoadHowMuch argument, which is either
	LoadAllTargets
	LoadUpTo Module
	LoadDependenciesOf Module
   which should be self-explanatory.  LoadDependenciesOf might go
   away in the future, it's necessary at the moment because it is
   used in the implementation of:

 - checkModule :: Session -> Module -> MessageHandler -> IO CheckResult

   which is currently the only way to get at the parsed & typechecked
   abstract syntax for a module.