Description:
------------
Fatal error: Class FooExtra could not implement interface IteratorAggregate in Unknown on line 0



Reproduce code:
---------------
class Foo implements
      IteratorAggregate, Iterator
{
   function rewind(){}
   function hasMore() {}
   function key() {}
   function current(){}
   function next() {}
   function valid() {}
   function getIterator() { return $this;}
}

class FooExtra extends Foo
{   function valid() {} }

Actual result:
--------------
Fatal error: Class FooExtra could not implement interface IteratorAggregate in Unknown on line 0