It turned out that doing all binding dependency analysis in the typechecker
meant that the renamer's unused-binding error messages got worse.  So now
I've put the first dep anal back into the renamer, while the second (which
is specific to type checking) remains in the type checker.

I've also made the pretty printer sort the decls back into source order
before printing them (except with -dppr-debug).

Fixes rn041.