UPnP is now used to request a port on the NAT be forwarded to the local machine.
This obviously only works for NATs that support UPnP, and thus is not a panacea
for all NAT-related connectivity issues.
Notable hacks in this patch include a transmit/receive UDP socket pair to work
around current protocol limitations whereby the full node assumes its peer can
receive on the same UDP port it transmitted from.
We added them thinking it'd be a good stepping stone towards an
asynchronous thin client, but it's used inconsistently and where
it used, the function is still synchronous, which is just confusing.
Anatoly Yakovenko
Michael Vines
Stephen Akridge
Rob Walker
Greg Fitzgerald
anatoly yakovenko