Core: Add "method" field to error list entry

To check what kind of validation rule was broken, so we could find a
difference between required or regex validation error raised.

Closes #1035

src/core.js

@@ -668,7 +668,8 @@ $.extend($.validator, {
 			}
 			this.errorList.push({
 				message: message,
-				element: element
+				element: element,
+				method: rule.method
 			});
 
 			this.errorMap[element.name] = message;