[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/php5/proxy/example.i

@@ -0,0 +1,12 @@
+/* File : example.i */
+%module example
+
+%{
+#include "example.h"
+%}
+
+/* Let's just grab the original header file here */
+
+%newobject CircleFactory;
+%include "example.h"
+