[Distutils] Determining if a module is in an egg or not

[Bob Ippolito]

I started refactoring py2app, modulegraph, etc. for setuptools and  
eggs.  After doing dependency resolution via modulegraph, py2app  
needs to know which of those dependencies are in eggs and where those  
eggs are so that it can just throw the egg (and its dependencies)  
into the application bundle instead of doing the normal py2app thing.

Is there an API to map __file__ paths to eggs?  It seems possible for  
zip and directory eggs by walking up os.path.dirname(__file__) and  
using find_distributions, but that doesn't seem to work for "setup.py  
develop" eggs.

-bob