Patch documents that empty dictionary is used to make ProxyHandler()
with disabled proxy autodetection. Empty constructor doesn't give the
desired effect.

P.S. An ideal approach would be, of course, to change the API. Even
though it can be changed drastically the simple hack would look like:

class ProxyHandler([proxies][, autodetect=False])

Seems like it is better to leave API for Py3K refactoring issue, like #1333