fix(jqLite): make attr() compatible with jQuery 1.6.4

The behavior of attr() getter and setter changed in jQuery 1.6 and now they treat element properties and attributes as two different things, but in order to not break everyone there is a partial backwards compatibility for checking and updating element properties as well. see http://api.jquery.com/prop/ for more info.

src/jqLite.js

@@ -255,9 +255,15 @@ forEach({
   attr: function(element, name, value){
     if (SPECIAL_ATTR[name]) {
       if (isDefined(value)) {
-        element[name] = !!value;
+        if (!!value) {
+          element[name] = true;
+          element.setAttribute(name, name);
+        } else {
+          element[name] = false;
+          element.removeAttribute(name);
+        }
       } else {
-        return element[name];
+        return (element[name] || element.getAttribute(name)) ? name : undefined;
       }
     } else if (isDefined(value)) {
       element.setAttribute(name, value);