New http support for libpurple

[Tomasz Wasilczyk]

Hi,

as we discussed before on devel at conference.pidgin.im, libpurple needs
to drop its own http queries support and get a dependence on dedicated
http support library. Without using such library, I may not be able to
implement some features, which need more sophisticated requests, than
libpurple offers.

There was two proposals: libsoup and libcurl. The first one had
dependency-related advantages, while the second one seems to be
generally better (see [1]).

I think, we should provide simple libpurple functions, for creating
and registering http queries:
- creating: just encapsulates function like curl_multi_init and
registers its output;
- registering: adds query handle to some list connected with certain
account - we should close such http connection when pidgin
disconnects; we could also watch such handle by ourselves, in our
thread.

Waiting for comments and decisions,
Tomek Wasilczyk

[1] http://curl.haxx.se/libcurl/libsoup.html