Hopefully these are correct, and clearerabout the
behaviour/pre-conditions of these methods.

Not sure how they got there, but Django doesn't use Jinja without
explicit configuration.

This matches a tweak made in 8765f761c995c31c9bff6287d881f0e9b5d0cfc5

There is only so much trackpad-driven yEd work one man can handle

I took the liberty of renaming ModuleFinder.STDLIB_DIRS to
_STDLIB_PATHS, since it felt like an implementation detail that
shouldn't be baked into a public API and stdlib can also be imported
from e.g. a zip file.

I also changed it to a set to handle any duplicates.

Fixes #86

The solution was that Mitogen's loader should emulate the behaviour of
ansible.executor.module_common, which restricts dependency scanning to
the ansible.module_utils namespace.