[php] Always use <?php to start .php file

A few files had just <? which only works when the short_open_tag option
is on.  It is on by default (at least in current PHP versions) and we
explicitly tell PHP not to read php.ini, but the PHP docs recommended to
avoid it, and PHP can be built with --disable-short-tags.

Examples/test-suite/php/exception_order_runme.php

@@ -1,4 +1,4 @@
-<?
+<?php
 require "tests.php";
 
 check::functions(array('is_python_builtin'));

Examples/test-suite/php/virtual_vs_nonvirtual_base_runme.php

@@ -1,4 +1,4 @@
-<? 
+<?php
 
 require "tests.php";