Reduce stack limit for stack_limit_015.phpt

The limit was too high with the new changes for 32-bit windows, apparently.

Author: iluuu1994

Zend/tests/stack_limit/stack_limit_015.phpt

@@ -9,7 +9,7 @@ if (!function_exists('zend_test_zend_call_stack_get')) die("skip zend_test_zend_
 --EXTENSIONS--
 zend_test
 --INI--
-zend.max_allowed_stack_size=128K
+zend.max_allowed_stack_size=64K
 --FILE--
 <?php