pex pulls in pre-release versions of libraries

[daveFNbuck]

I recently had an issue where my production build stopped working because it picked up a pre-release version of protobuf. pex protobuf will pick up version 3.2.0rc2 right now, while a pip install will pick up 3.1.0.post1. I didn't expect this to happen and there doesn't appear to be a way to change the behavior.

[daveFNbuck]

pip seems to be following PEP 440 and defining stable releases to exclude pre-releases (those including a, b, or rc in the version identifier) and developmental releases (those with dev followed by a number at the end).

[wickman]

I think this is a dupe of #28. y/n?

[daveFNbuck]

Yes, I missed that one in my search.