1. Use SIGHUP for restart instead of SIGINT, and use SIGUSR2 to reopen
   the log file instead of SIGHUP.  This is the same standard as for
   the Zope server.

2. When using zdaemon, let zdaemon write its pid to the zeo_pid file;
   when not using zdaemon, write only our own pid to the zeo_pid
   file.  Never write two pids.