[m-rev.] for review: merge integer token representations in the lexer

[Zoltan Somogyi]

> Ignore that, it's a dreadful idea -- those types are part of the
> public interface of the term module.

Given that these types are effectively describing an aspect
of a set of soon-to-be-added builtin types, would anyone
object moving them from term.m to builtin.m?

Zoltan.