/*
 * Return the filename of a Fam::Event object.
 *
 * Note: for directory monitors, this method returns the path of the
 * file relative to the monitor directory, not the full path.
 * 
 * Aliases:
 *   Fam::Event#file
 *
 * Examples:
 *   path = ev.filename
 *   path = ev.file
 *
 */
static VALUE fam_ev_file(VALUE self) {