[PHP] Add support for PHP7.

PHP5's C extension API has changed substantially so you need to use
-php7 to specify you want PHP7 compatible wrappers.
Fixes https://github.com/swig/swig/issues/571

Examples/test-suite/php5/abstract_inherit_ok_runme.php

@@ -0,0 +1,12 @@
+<?php
+
+require "tests.php";
+require "abstract_inherit_ok.php";
+
+check::classes(array(Foo,Spam));
+$spam=new Spam();
+
+check::equal(0,$spam->blah(),"spam object method");
+
+check::done();
+?>