Pass tests in es5 test262 ch15.2.3.3 (except for URI-related features)

- Add every builtin function templates in es5
- Modification on Makefile target "check" should not trigger rebuild
- Add JSON object
- Implement some toString functions
- Initialize m_value properly in ObjectPropertyDescriptor constructor

src/runtime/Object.cpp

@@ -89,6 +89,8 @@ ObjectPropertyDescriptor::ObjectPropertyDescriptor(ExecutionState& state, Object
     if (desc.hasValue()) {
         m_value = desc.value(state, obj);
         hasValue = true;
+    } else {
+        m_value = Value();
     }
 
     desc = obj->get(state, ObjectPropertyName(strings->get));