Improve factory shutdown procedures

* Set process group id in glideFactory
* Set signal handlers to default for children that execute writeStats
  - We normally trap SIGTERM and raise a KeyboardInterrupt so we can
    shut things down cleanly.  However, since the low-level write
    routines catch exceptions and abort their current process, a SIGTERM
    most of the time just aborts the current line of log-writing and goes
    on with the next (!).  Since we don't shut the writeStats processes
    down cleanly anyway, let's just have the system terminate them.