Find way to deal with HTTP_PROXY (and friends) env configs when running tests

[jfhbrook]

If you accidentally have HTTP_PROXY-related env vars configured, this can severely confuse the tests.

Probably the best approach is to document this edge case. If you run into this issue, the easiest thing to do is probably

HTTP_PROXY='' npm test

or similar.

See: https://github.com/jfhbrook/node-ecstatic/pull/175

[jfhbrook]

This might be solve-able by making the tests use pickleback, sidestepping any request issues.