Tests for new node environment setting

[etianen]

The tests.py module should ideally test both, but should skip the rhino/node tests when that environment is not available.

[jmbowman]

I thought about this when writing my patch, but haven't yet come up with a solution that seems satisfying. You can configure different tests to run in different environments, but verifying that the correct one was actually used is a little harder; the output should be the same in either case unless you also specify different optimizers. I guess just having tests that correctly produce output using what they think is the configured environment is a start.

[etianen]

Now that #7 has made the default optimizer uglify, these tests should also use the closure compiler when testing the rhino environment.