[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/pointer_reference_runme.php

@@ -0,0 +1,18 @@
+<?php
+
+require "tests.php";
+require "pointer_reference.php";
+
+$s  = pointer_reference::get();
+check::equal($s->value, 10, "pointer_reference::get() failed");
+
+$ss = new Struct(20);
+pointer_reference::set($ss);
+$i = Struct::instance();
+check::equal($i->value, 20, "pointer_reference::set() failed");
+
+check::equal(pointer_reference::overloading(1), 111, "overload test 1 failed");
+check::equal(pointer_reference::overloading($ss), 222, "overload test 2 failed");
+
+check::done();
+?>