Description:
------------
Seems PHP does not support exception catching by parent interface (not by parent classes). Why? This is a very powerful method to classify exceptions in programs. 

Documentation says that while comparing type in catch block 'instanceof' operator is used, but following test shows that it is wrong.

I found corresponding code in the source, zend_execute.c:2866, and it searches for parent classes only. Why not use instanceof_function?

Do you have any perspectives about this problem? Can I wrote in my book that PHP will support "interface catching" in the future?

Reproduce code:
---------------
<?
interface E {}
class A extends Exception implements E {}
try {
  throw new A();
} catch (E $e) {
  echo $e;
}
?>

Expected result:
----------------
prints exception data

Actual result:
--------------
Fatal error: Uncaught exception