Re-expose formatDate on the plot object.

jquery.flot.time.js

@@ -361,4 +361,10 @@ for details.
 		version: '1.0'
 	});
 
+	// Time-axis support used to be in Flot core, which exposed the
+	// formatDate function on the plot object.  Various plugins depend
+	// on the function, so we need to re-expose it here.
+
+	$.plot.formatDate = formatDate;
+
 })(jQuery);