Added basic support for foreign export dynamic.

Many aspects of it are still broken:
* Only supports x86-linux.
* The range of allowable types is small: Char Int Float Double
  Addr and Word.
* Adjustor thunks are never freed.
* Returning Doubles or Floats doesn't work at all.

I expect to fix some of these shortly.  foreign import also
needs redoing, so it can accept any number of arguments of
any type.

Also:
* Fixed setRtsFlags in Evaluator.c to make it endian-independent.
* Fixed raisePrim in Evaluator.c so things like division by zero,
  array index errors, etc, throw an exception instead of
  terminating StgHugs.  raisePrim is renamed makeErrorCall.