Description:
------------
Consider a situation when an abstract class (or an interface) is defined and a 
concrete class that extends it. If we get instantiate a ReferenceClass object for 
the abstract class (or the interface), we can then get an ReferenceMethod instance 
for the abstract method.

Unfortunately, calling the ReferenceMethod::invoke() method for an instance of the 
concrete class throws a ReflectionException ("Trying to invoke abstract 
method...").

Test script:
---------------
<?php
abstract class A
{
        public abstract function doA();
}

interface IB
{
        function doB();
}

class B extends A implements IB
{
        public function doA()
        {
                echo 'A is done.';
        }

        public function doB()
        {
                echo 'B is done.';
        }
}

$b = new B();
$b->doA();
$b->doB();

$refA = new \ReflectionClass('A');
$refDoA = $refA->getMethod('doA');
$refDoA->invoke($b);

$refIB = new \ReflectionClass('IB');
$refDoB = $refIB->getMethod('doB');
$refDoB->invoke($b);
?>


Expected result:
----------------
The invocation of the method on an instance of the concrete class should succeed.

Actual result:
--------------
PHP Fatal error:  Uncaught exception 'ReflectionException' with message 'Trying to 
invoke abstract method ...()' in ...:..