Naming changes in External Core

Two changes:
- Top-level bindings in a given module are now printed as a
  single %rec group. I found that in External Core generated from
  optimized code, nonrec bindings weren't being printed in
  dependency order. Rather than fixing that, I decided to not
  even pretend to preserve dependency order (since there's
  recursion between modules anyway.)

- Internal names are now printed with their uniques attached
  (otherwise, GHC was printing out code with shadowed bindings,
  and this isn't supposed to happen in External Core.)