Description:
------------
As reported by dmitry in https://bugs.php.net/bug.php?id=63066 there currently are issues with yield interruptions in nested method calls.

The following code:

<?php
class A {
    function foo() {
        echo "Called A::foo\n";
    }
}

class B {
    function foo() {
        echo "Called B::foo\n";
    }
}

function gen($obj) {
    $obj->foo($obj->foo(yield));
}

$g1 = gen(new A);
$g1->current();

$g2 = gen(new B);
$g2->current();

$g1->next();

Will output:

Called A::foo
Called B::foo
[Fri Sep 21 16:49:14 2012]  Script:  '/home/nikic/dev/php-src/t26.php'
/home/nikic/dev/php-src/Zend/zend_vm_execute.h(949) :  Freeing 0xB77579F0 (20 bytes), script=/home/nikic/dev/php-src/t26.php
=== Total 1 memory leaks detected ===

The issue is that generators currently only back up the argument stack (the main VM stack), but don't back up the argument type stack EG(arg_types_stack). This stack contains object and fbc.

So when two generators with nested method calls are intermixed the VM mixes up the different objects/fbcs (and if a generator is closed during the nested method call the object leaks).