- there were reports of errors in FreeBSD (I could only reproduce some) and Gentoo without IPv4 support (I don't have a VM for testing ready) - adds an exception handler for double task_done in case sender thread has to close prematurely (I saw this triggered on FreeBSD 11) - listening socket opening error handler was broken (triggered if you can't open a socket with both IPv4 and IPv6 support) - error handler for socket.accept. Reported on FreeBSD 10.3 - fixes #854