Description:
------------
When extending abstract classes you are not allowed to change an abstract method's signature to a compatible one. This works perfectly fine for concrete classes though.

Test script:
---------------
//This code works:

class A { 
    public function a () {}
} 

class B extends A { 
    public function a ($t = false) {}
}

//this code throws an error:

abstract class A { 
    abstract public function a ();
} 

abstract class B extends A { 
    abstract public function a ($t = false);
} 

Expected result:
----------------
Extending an abstract method should behaves consistently with extending concrete methods

Actual result:
--------------
Fatal error:  Can't inherit abstract function A::a() (previously declared abstract in B)