add stat logic to the static file rule

- this emulates Python's WatchedFileHandler for logging, where we check
  the inode of our logfile path to see if it was changed out from underneath
  us by an external tool like logrotate.

  This allows applications that use an external tool for log rotation/compression
  to have a simple log configuration and not have to worry about calling zlog_reload
  to reopen the new file after the external tool has run.
Merge pull request #42 from wynnw/feature/watched-file-mode

Change to the static file rule to emulate python's WatchedFileHandler mode when used with external log rotation