[packagekit] Adding more proxy settings

[Richard Hughes]

In https://bugs.freedesktop.org/show_bug.cgi?id=33009 I've been asked
to support the "no_proxy" use case where there is a list of IPs or
domains that should go direct rather than through the proxy server. I
don't use this myself, but apparently a lot of people do.

Unrelated, I also had someone ask if they can get the https proxy in a
backend in a private mail to me a few months back.

I'm thinking of extending the SetProxy method with two additional
string parameters, ignore_proxy and https_proxy.

For backwards and forwards compatibility, I was going to name the
method SetProxy2 and just remove the original SetProxy when we fork
for 0.7.

Comments?

Richard.