Set close-on-exec in attempt to head off GitHub issue #61
Was not closing _shutdownSignalPipe in UnixEthernetTap either...
.... aaaaaand... GitHub issue #61 was caused by the fact that we were no longer deleting taps on Windows!
Some cleanup, and use best (not first) UDP addresses for NAT-t VERB_RENDEZVOUS computation.
Yet more cleanup to TCP logic, this time adding a master switch and adding UDP preference in send().
More logic cleanup and some documentation / comment improvements.
Probable fix for GitHub issue #63 - do not unite() if either path is TCP, since doing so can result in asymmetric failed NAT-t over UDP if one side has a firewall that permits outgoing UDP but not incoming.
Prevent recursive transit of ZeroTier packets, toward GitHub issue #56
More toward GitHub issue #56
VERSION 0.8.2

This version fixes a few more issues with TCP tunneling including GitHub issue #63.
It also adds automatic announcement and location of peers on physical LANs (GitHub
issue #56) which should greatly improve performance if you happen to be on the same
LAN or WiFi network as another peer. It can take 60 seconds or so for this to occur,
but it should.