Add shutdown signaling to unix socket, removing quit delay in tdtool

Not sure if something else depends on the sockets returning final data, while shutting down?

Works fine on FreeBSD at least, might want to test on other *NIX/Linux.

Solves the problem with tdtool hanging for a few seconds on exit (since EventSocket in Client::run is blocking; not even used in tdtool?)

This fix is very similar to #5, but on FreeBSD just using SHUT_RD did not do the trick.