  The program is intended to be run by cron every hour.

    42 * * * * perl /usr/local/bin/mirmon -q -get update

  It quietly probes a subset of the sites in a given list,
  writes the results in the 'state' file and generates a web page
  with the results. The subset contains the sites that are new, bad
  and/or not probed for a specified time.

  When no 'get' option is specified, the program just generates a 
  new web page from the last known state.

  The program checks the mirrors by running a (user specified)
  program on a pipe. A (user specified) number of probes is
  run in parallel using nonblocking IO. When something can be
  read from the pipe, it switches the pipe to blocking IO and
  reads one line from the pipe. Then it flushes and closes the
  pipe. No attempt is made to kill the probe.

  The probe should return something that looks like "1043625600\n",
  that is, a timestamp followed by a newline. The exit status of
  the probe is ignored.
