[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/value/example.i

@@ -0,0 +1,17 @@
+// Tests SWIG's handling of pass-by-value for complex datatypes
+%module example
+
+%{
+#include "example.h"
+%}
+
+%include "example.h"
+
+/* Some helper functions for our interface */
+%inline %{
+
+void vector_print(Vector *v) {
+  printf("Vector %p = (%g, %g, %g)\n", (void *)v, v->x, v->y, v->z);
+}
+%}
+