System module has a watchdog call which is not using WATCHDOG_ERROR constant

The system module has a watchdog call which is not using the proper constant for a WATCHDOG_ERROR. This causes PHP warnings as the error level used is a string and syslog expects an integer.

Original line:
watchdog('file system', 'Could not delete temporary file "%path" during garbage collection', array('%path' => $file->filepath), 'error');

Should be:
watchdog('file system', 'Could not delete temporary file "%path" during garbage collection', array('%path' => $file->filepath), WATCHDOG_ERROR);