mdo-trex stuff

I was experimenting with the qualified names and mdo-trex stuff. Found out
the following:

1. The following code should work with all import variants.
   It "used" to work with the third variant only
   Right now, it doesn't work with any of them!
----------------------------------------------------------------
-- should work with all forms of import below:
-- import qualified Trex as Tr
-- import qualified Trex 
import Trex 

t = let r1 = (a=True,b=False)
	r2 = (b=False,a=True)
    in r1 == r2
----------------------------------------------------------------

 I guess functionality similar to "mdoLoad()" is required to
 handle the trex case correctly as well.

 Note: if you type a similar expression at top-level interpreter,
 then it works. 

2. If you simply do:

       hugs -98 /usr/local/src/hugs98/lib/hugs/Trex.hs 

   you get a weird error.

3. We've nuked MonadRec.hs from sources, but Siggy's new code works
   with both MonadRec and Control.Monad.Fix. 

   Either we should add MonadRec back to lib/exts, or just not
   support the old naming anymore. (I'm not sure what's the
   right thing there.)

-Levent.