--------------------------
	Fix export-calculation bug
	--------------------------

Ross points out that in
 	module M where
 	import List as M
 	sort = "foo"

there is no conflict in the export list. GHC used to treat this
like

	module M( module M ) where ...

which is wrong, wrong, wrong.

Now fixed.   Test in modules/mod200.hs

Some other small tidying up (notably in GRE.gre_parent).