External Core: print function types correctly, improve newtype pretty-printing

- In a previous patch I broke the printing of fully-applied arrow
types (e.g., "a -> b" was "(ghczmprim:GHCziPrim a b)") by z-encoding
package names and not updating the primitive module name as defined in
External Core accordingly. Fixed. (Mega sigh...)

- Make newtype decls print slightly more readably.