If the same method name is implemented in a parent class then the
subclass can't have more required parameters than that or else we
get a compatibility error when the module is loaded.
The testsuite wasn't catching this problem because it was no longer
trying to load the modules for testcases without _runme.php, because
the mechanism to do that relied on there being a generated .php
wrapper, which we no longer have by default. Fix that to provide a
regression test for this fix.
See #2151
