The package_template fixture was causing me too many problems, and it's more than we really need for the purposes it's being used for at this point.  So for the version tests I just created a new test package that performs the bare minimum function.  Also added a utility function for cleaning up modules imported during tests.
Cleanup unused import
Cleanup this little snippet.  I'm not sure what purpose it originally served but it doesn't seem to be necessary anymore for the tests to pass?  In any case, it was causing conflicts with py.test's assert rewriting code :(
When running tox, clean up the build area between tests (otherwise the generated version.py can actually cause syntax errors when running the tests with other Python versions)
Should implement #87
Merge pull request #87 from embray/issue-87

version.py does not hard-code githash for releases