Description:
------------
I think this fatal error is needless. 

Interface implementors can append optional parameter:

interface IAnimal
{
	function speak();
}

class Dog implements IAnimal
{
	function speak($optional = NULL)
	{
		echo 'Bark!';
	}
}

class Labrador extends Dog
{
	function speak($optional = NULL, $anotherOptinal = NULL)
	{
		...
	}
}


That's correct behaviour. But the same behaviour is unallowed for interface extenders. 



Reproduce code:
---------------
interface IAnimal
{
	function speak();
}


interface IHuman extends IAnimal
{
	function speak($language = NULL);
}




Expected result:
----------------
no error

Actual result:
--------------
Fatal error: Can't inherit abstract function IAnimal::speak() (previously declared abstract in IHuman)