Added support for synchronous requests.

This is needed to address the fact that QtWebKit from v2.2 forwards no longer
creates its own event loop to handle such requests. Instead it expects QNAM, or
any reimplementation, to deal with it on its behalf. Credit goes to Pierre
Rossi for discovering this issue.

BUG: 231932
FIXED-IN: 4.7.0
REVIEW: 101876

(cherry picked from commit c3e213d9)