This updates the GitHub test suite to check all the HTTP requests

performed, ensuring that we're calling each API we expect with the

correct data in the correct order, and to ensure that payloads are sent

as bytes and not Unicode strings.
It also does a better job of checking results, and simplifies a few

payloads.
This uncovered problems where we were using ugettext_lazy for some

exceptions in GitHub, which this change also fixes.
Docstrings for tests and utility functions have been added/updated to

better fit modern docstring formats.

Unit tests pass.