saving state in a pck pickle file, and doing an incremental parse the
next time.  Specifically:

Added -f and -r flags.  The -f flag points to the pickle state file
(by default ./zeoqueue.pck).  The -r flag simply removes this file.
This is useful for log rotation in the cron job, and yes rm would have
been fine, but this option was requested by customers.

process_file(): Added to Status class so that the processing is done
here, where we can seek to a stored file position.

Also added the secret -0 option for testing, which suppresses the file
position seek (useful when the log file is split into chunks).

Return the number of blocked clients as the exit status code.