I found an ugly workaround for my stalling problem: set up an
independent timer that runs a curl_multi_socket_all loop
unconditionally every fifteen seconds or so. That's certainly
not an ideal solution, but at least it means the problem isn't
an absolute show-stopper. I managed to get that local-proxy
thing I mentioned earlier up an running, and so far it seems
to be doing surprisingly well.

Also, thanks for merging the timer patch, mentioning me in the
ChangeLog, and especially for not asking me to write the docs :-)

I also noticed you added ghiper.c to curl/docs/examples.
Here is a revised version that uses the timer callback....