[php] Fix handling of multi-module cases

Look up unknown base classes using SWIG_MangledTypeQueryModule().

Revert to using SWIG_TypeCheck() instead of SWIG_TypeCheckStruct()
as the latter doesn't seem to work for this case (at least for PHP
right now).

Add mod_runme.php as a regression test for this.

Adjust the PHP test harness not to set up reflection for the module
unless it's actually needed for a testcase.  Currently the approach
to find the module name doesn't work for multi-module testcases.

See #2126

Examples/test-suite/php/mod_runme.php

@@ -0,0 +1,9 @@
+<?php
+
+require "tests.php";
+
+$c = new C();
+$d = new D();
+$d->DoSomething($c);
+
+check::done();