0b56d603c2
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.