- Add pygolang/buildout-dev.cfg that overrides [pygolang] to use the
  software from git checkout.

- Add pygolang/test.cfg that is software-release to create a test
  instance to be run under testnode. This software release uses
  just-added stack/nxdtest.cfg to help itself on this task, so the code
  in pygolang is minimal.

A new section [python-interpreter] is added, because python interpreters
that zc.recipe.egg generates don't process `-m args` correctly and
handle subprocess well. I had to workaround that with code from
gpython.pymain to be able to run `python -m pytest --<pytestarg>` and to
spawn children processes with preserving sys.path. Comments around and
inside [python-interpreter] has more details on this topic.