only add a module if compile_and_import_proto returned one
Fix up importing a compiled protobuf files
In case we attempt to import a _pb2.py directly, we overlooked any potential
dependent imports it relied on (which we subsequently overlooked to copy
over into the new temporary directory as well). Rather than copying these over,
we attempt to just import them directly with an updated PYTHONPATH.
recursively select all protobuf message types in all imported modules (not just the selected one)