Cleanup of RnExpr, RnEnv and RnSource

[Jan Stolarek]

Dear all,

RnExpr, RnEnv and RnSource (in compiler/renamer) declare locally:

\begin{code}
-- XXX
thenM :: Monad a => a b -> (b -> a c) -> a c
thenM = (>>=)

thenM_ :: Monad a => a b -> a c -> a c
thenM_ = (>>)
\end{code}

and then use these aliases instead of >>= and >>. These were introduced by Ian in 
6c7b41cc2b24f533697a62bf1843507ae043fc97 in 2008 and later partially cleaned up by Simon in 
f0c99958649b8909612b1b9c9b48aad970dfce05 in 2009. Would there be objections if I cleand this up 
(ie. remove thenM and thenM_ and use >>= and >>)? Is anyone doing any substantial changes on any 
of these files and suspects that this could introduce merge conflicts for him? I'm at the moment 
changing some things in RnExpr, so doing this will only add little extra work for me and I'd like 
to take this oportunity to have cleaner code.

Janek