Support unix domain socket connections on Unix

Since we support pipe connections with 1.1.3, we might also support Unix domain socket connections. ConnectorJ does not provide support for them out of the box (and Java does not support unix domain sockets yet),
however for ConnectorJ there are a couple of 3rd party JNI based solutions (JUDS, junixsocket). JNI is not very convenient to use, because it requres infrastructure for native compilation and distributing shared libraries.

A better solution is JNA (Java native access), as eliminates native programming entirely . This would still add an extra runtime dependency on 3rd party for those who like to use unix domain sockets (but the library is well established meanwhile)