For Python 3.4:

Maybe rather than raising ImportError, we could issue warning to notify the users that names from the __main__ namespace could not be loaded and make the init_module_attrs return early.

This way a multiprocessing program that only calls functions defined in non-main namespaces could still use the new "start method" feature introduced in Python 3.4 while not changing the Python 3.3 semantics for windows programs and not relying on any deprecated hack.