[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/add_link_runme.php

@@ -0,0 +1,22 @@
+<?php
+
+require "tests.php";
+require "add_link.php";
+
+// No new functions, except the flat functions
+check::functions(array(new_foo,foo_blah));
+
+check::classes(array(Foo));
+
+$foo=new foo();
+check::is_a($foo,foo);
+
+$foo_blah=$foo->blah();
+check::is_a($foo_blah,foo);
+
+//fails, can't be called as a class method, should allow and make it nil?
+//$class_foo_blah=foo::blah();
+//check::is_a($class_foo_blah,foo);
+
+check::done();
+?>