Testing enhancements

• Ensure the Newton command-line adapter works with Nashorn.
• Add Nashorn to the test matrix.
• Merge Sauce Labs Automated Testing #49; update our list of supported environments to match those provided by Sauce.
• Switch to the new Travis container-based infrastructure.
• Add Browserify, webpack, and r.js integration tests
• Improve the noConflict and runInContext tests. a7f5fe8 fixed a regression where runInContext would return early for environments that supported JSON natively, but this wasn't caught by the tests.