[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/conversion_namespace_runme.php

@@ -0,0 +1,13 @@
+<?php
+
+require "tests.php";
+require "conversion_namespace.php";
+
+check::classes(array("Foo","Bar"));
+$bar=new Bar;
+check::classname("bar",$bar);
+$foo=$bar->toFoo();
+check::classname("foo",$foo);
+
+check::done();
+?>