--------------------------
	Tidy up arity propagation (the saga continues)
	--------------------------

Turns out that it's not as easy as I thought.

The code generator was assuming that (not . isLocalName) was enough to
identify an imported thing (whose CgInfo should be right), but that's
not true.  Needs more thought.

Meanwhile, I've made the code generator a bit more sensible about how
it looks things up.  But there's still a problem for GHCi: the
unfoldings in the TypeEnv won't have CgIdInfo stuff.  Sigh.  Thinks.