more descriptive __name__ for curry_context'd things

If you ask a build_file_aliases curry_context-thingy for its __module__.__name__ , it says pants.base.build_file_aliases.<lambda>

That seems less useful than, say, pants.base.build_file_aliases.curry_context.pants.backend.python.python_requirements.python_requirements

Testing Done:
./build-support/bin/publish_docs.sh

https://travis-ci.org/pantsbuild/pants/builds/31350494

Bugs closed: 354

Reviewed at https://rbcommons.com/s/twitter/r/756/