Description:
------------
On the one hand it's possible to create a RecursiveIteratorIterator out of an 
object that implements IteratorAggregate *and* that returns an object 
implementing 
RecursiveIterator for IteratorAggregate::getIterator(). That's fine.

On the other hand, if RecursiveIterator::getChildren() returns an object that 
implements IteratorAggregate *and* that returns an object implementing 
RecursiveIterator for IteratorAggregate::getIterator() it gives this error:

Fatal error: Uncaught exception 'UnexpectedValueException' with message 'Objects 
returned by RecursiveIterator::getChildren() must implement RecursiveIterator'

It would be nice if both, the iterator object in instantiating 
RecursiveIteratorIterator and the return object for 
RecursiveIterator::getChildren() would be compatible in the sense that both 
would 
allow an object implementing IteratorAggregate.

Right now, only the constructor allows this, but getChildren() does not allow 
IteratorAggregate.

For completeness of this report, if an invalid iterator is given on 
instantiating 
a RecursiveIteratorIterator, the error message is:

Fatal error: Uncaught exception 'InvalidArgumentException' with message 'An 
instance of RecursiveIterator or IteratorAggregate creating it is required'

Test script:
---------------
(my test script is a little larger, I can provide one upon request)