Comment 14 for bug 1335116

All right. Since the libproxy project seems to be more or less dead for the moment, I tried the other option: use code from /usr/lib/python2.7/dist-packages/ubuntu-sso-client/ubuntu_sso/utils/webclient/gsettings.py as mentioned in comment #11.

You can find the result of my tinkering in attached patch file.

Please note that I am not a python developer. I am totally ignorant of any python naming conventions, so you might need to make some adjustments.

This patch seems to work in my situation.
It can handle manually specified proxies. It cannot, however, handle automatically defined proxies, e.g. those based on PAC scripts.