LP#1268619: websocket translator idle timeout / graceful shutdown

LP#1268619: websocket translator idle timeout / graceful shutdown

Added support for an idle timeout and idle check interval configuration
variables.  These allow each websocket apache process to kick off
clients that have been connected and are idle for too long, thus hogging
a process unnecessarily.

Added a SIGUSR1 signal handler which forces the idle timeout to be very
low and a short re-check period so that the client can be kicked as soon
as there are no open conversations.

Signed-off-by: Bill Erickson <berick@esilibrary.com>