Monkey-patch url.parse in test setup

url.parse in node < 0.8.24 passed already-parsed URL's (objects)
through, rather than throwing an error.  node >= 0.8.24 throws an error
for these (which is arguably cthe correct behavior). However, Zombie.js
1.4.1 sometimes tries to re-parse already parsed urls.

This commit monkey-patches "url.parse" to survive this by bringing back
the old behavior of passing non-strings through.