original patch submitted in 2006 to debian mailing list:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=392848%29#12
this version was rebased to git and updated by Russ Dill <russ.dill@gmail.com>
in 2015 (the original patch used a different config file format).
as discussed in #40.
commit message by @rofl0r.
There are frequent questions "what does 'No proxy for ...' mean?"
on the mailing list and IRC. Be more specific. (No upstream proxy ...)
Correspondingly, log "Found upstream proxy ... for ..."
