Refs #21. Added support for virtualenv 1.8.2, 1.8.3 and 1.8.4. There are issues with 1.8 and 1.8.1
Refs #21. Added script to aide in local testing against different versions of virtualenv
Refs #21. Updated travis configuration to test against virtualenv 1.8.2, 1.8.3 and 1.8.4
Merge pull request #21 from PolicyStat/issue_21

Update requirements to include support for virtualenv 1.8.4 and others