> why regrlib.py at all?  Why isn't the code in regrtest.py?

It was for a few related reasons.  It was primarily to make it easier to reason about testing regrtest, and to avoid at the outset any pitfalls that might arise from the circularity of regrtest testing itself.  For example, the regrtest module seems to carry a fair bit of state and top-level code, whereas the "library" module being added would be stateless.  It would also let us maintain an obvious line between what is tested and what is not.

There was no discussion of creating a package.  However, if we go this route I would foresee moving functionality from regrtest to the library module as we expand the amount of regrtest-support code under test.