[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/director_string_runme.php

@@ -0,0 +1,34 @@
+<?php
+
+require "tests.php";
+require "director_string.php";
+
+// No new functions
+check::functions(array(a_get_first,a_call_get_first,a_string_length,a_process_text,a_call_process_func,stringvector_size,stringvector_is_empty,stringvector_clear,stringvector_push,stringvector_pop,stringvector_capacity,stringvector_reserve));
+// No new classes
+check::classes(array(A,StringVector));
+// now new vars
+check::globals(array(a,a_call,a_m_strings,stringvector));
+
+class B extends A {
+  function get_first() {
+    return parent::get_first() . " world!";
+  }
+
+  function process_text($string) {
+    parent::process_text($string);
+    $this->smem = "hello";
+  }
+}
+
+$b = new B("hello");
+
+$b->get(0);
+check::equal($b->get_first(),"hello world!", "get_first failed");
+
+$b->call_process_func();
+
+check::equal($b->smem, "hello", "smem failed");
+
+check::done();
+?>