Leaks redux

For now, this branch contains:

 * make the build fail if jslint is not happy
 * fix the travis build, by pinning http-proxy to a not-broken version
 * heavily enhanced tests, including a new test to reproduce our leakage issue (PUT /dev/urandom)

This is safe IMO (save http-proxy possible underlying issues...).

Having this merged fast, just after your memorymonitor PR would be cool, as the upcoming work (worker cleanup) will likely be more risky.