Description:
------------
The attached patch allows extending AMQPExchange and AMQPQueue for testing 
purposes. Unit testing frameworks like PHPUnit allow mocking of objects often by 
generating a child class to the mocked class and overloading each method. As 
overloading declare() in userland is not possible (due to "T_DECLARE" being a 
lexer token by itself) it is necessary for those frameworks to allow calling the 
declare()-method without segfaults. The attached patch will make declare() fail 
non-fatal and return null if the AMQPExchange/AMQPQueue object has not properly 
been initialized. Without this patch unit testing PECL amqp dependent classes is 
nearly impossible.

Test script:
---------------
<?php
class FakeExchange extends AMQPExchange
{
   public function __construct()
   {}
}

$exchange = new FakeExchange();

$exchange->declare();