Description:
------------
Presence of __invoke causes  is_callable($obj, '__construct') returns true, 
instead of false when it's called out of class scope.

Also, is_callable('class', '__construct') yields true even if __construct is set 
to protected (which is clearly not connected with __invoke issue, but I suppose 
that is caused by the same underlying problem).

Although setting __construct private/protected seems a little bit pervert, if it 
is not interdicted by language semantics, visibility testing should give good 
results. 

Test script:
---------------
class Singleton {
		protected static $aInstances = array();
		final protected function __construct(){}					
		public static function getInstance(){
    		$sClassName = get_called_class();
			if (!isset(static::$aInstances[$sClassName])) {
				static::$aInstances[$sClassName] = new $sClassName();		
			} // if
        	return static::$aInstances[$sClassName];		
		} // getInstance
	} // class
	
	class SingletonWithInvoke extends Singleton {			
		final protected function __invoke(){}	
	} // class
			
	var_dump(is_callable(Singleton::getInstance(), '__construct'));
	var_dump(is_callable(SingletonWithInvoke::getInstance(), '__construct'));
	var_dump(is_callable('Singleton', '__construct'));	
	var_dump(is_callable('SingletonWithInvoke', '__construct'));

Expected result:
----------------
bool(false) bool(false) bool(false) bool(false)

Actual result:
--------------
bool(false) bool(true) bool(true) bool(true)