proxy_test.py: Moves tornado curl_httpclient import to later.
Splits http module into http submodules.

Splits into modules http.client, http.connection, http.request,
http.util. Moves web module into http.web.
Updates backport.conf for http package.
http/client.py: Allows Recorders on initializer and fetch method.
proxy.py: Adds ProgressRecorder on debug runner.