innodb_status_file startup option lacks variable(s) and proper documentation

This feature dumps every ~20secs the InnoDB engine status on a file on the datadir, on the official MySQL documentation it is documented as "writing periodically the output of SHOW ENGINE INNODB STATUS" without specifying its recurrence.

This startup variable also doesnt have a corresponding runtime variable and it is not possible to configure neither its output filename nor the delay between two dumps and having the ability to activate/deactivate the feature without having to restart the server could also be interresting.

The code that defines the delay between two dumps on 5.5.30 : http://bazaar.launchpad.net/~maria-captains/maria/5.5/view/3749/storage/innobase/srv/srv0srv.c#L2187

Another possibility would be to replace it with a non engine-specific variable as other storage engines might also have engine status inforations (its the case for TokuDB for example) or that could dump informations from P_S/I_S.