- When both IPv4 and IPv6 plugins return a socket, use the IPv6 one if
IPV6_ONLY can be turned off. It is supposed to be off by default, and
it actually is. Unfortunately, OpenBSD and NetBSD people think
network software programmer like us are too stupid to use this
feature properly, so they just removed it. Lets say the most stupid
are not always the ones one think. Also, Windows doesn't support this
yet. On all these OSes, keep the old behavior; that is prefer IPv4.
Closes #166.