Pylons/pyramid — pull request #1015 by tseaver (2013-05-09 20:52:35+00:00)
Title: Implement PEP302 API in PackageOverrides as '__loader__'.

Proxy to the '__loader__' set by the importer, if present. Otherwise,
raise NotImplementedError.

We cannot raise in the presence of an existing '__loader__', because Python 3.3.x sets one for any module. So, we need to pretend to be one by proxy.