using Thread.interrupt() methods external to switch, along with  corresponding while test, finally killed threads

Numerous threading complications unraveled, more stable operation, watch out for senderThread closing

javadoc tweek, SuppressWarnings about thread sleeping in loop (so that programs employing it don't get deprecation warnings)

fix threading/race condition causing intermittent socket errors by refactoring socket creation from send/receive threads, synchronized to avoid interleaved reentry