Description:
------------
A notice is triggered when a child class of OAuth accesses its own attributes.

Reproduce code:
---------------
<?php
class Foo extends OAuth
{
    protected $foo = 'bar';

    public function getFoo()
    {
        return $this->foo;
    }
}

$foo = new Foo('key', 'secret');
var_dump($foo->getFoo());

Expected result:
----------------
string(3) "bar"

Actual result:
--------------
sb@vmware ~ % php Foo.php 

Notice: Undefined property: Foo::$foo in /home/sb/Foo.php on line 8

Call Stack:
    0.0003     680784   1. {main}() /home/sb/Foo.php:0
    0.0005     685608   2. Foo->getFoo() /home/sb/Foo.php:13

NULL