-------------------------------
	Fix the dreaded export list bug
	-------------------------------

With unfailing regularity I manage to get the following wrong:

	module A(f) where 
	  f = ...

	module B(f) where
	  import A(f)

We must ensure that if A.f changes its type (etc) then B.hi
gets changed, so that people who import B will get recompiled.

There's a large comment with RnIfaces.mkImportInfo, and some
reorganisation in Rename, with a few mainly cosmetic consequences
in RnEnv.

[Simon: I think this will fix the 'OccurAnal not recompiled' problem.]