[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/reference/runme.php

@@ -0,0 +1,49 @@
+<?php
+
+# This file illustrates the manipulation of C++ references in PHP.
+
+require "example.php";
+
+# ----- Object creation -----
+
+print "Creating some objects:\n";
+$a = new Vector(3, 4, 5);
+$b = new Vector(10, 11, 12);
+
+print "    Created a: {$a->as_string()}\n";
+print "    Created b: {$b->as_string()}\n";
+
+# ----- Call an overloaded operator -----
+
+# This calls the wrapper we placed around
+#
+#      operator+(const Vector &a, const Vector &) 
+#
+# It returns a new allocated object.
+
+print "Adding a+b\n";
+$c = example::addv($a, $b);
+print "    a+b ={$c->as_string()}\n";
+
+# ----- Create a vector array -----
+
+print "Creating an array of vectors\n";
+$va = new VectorArray(10);
+
+print "    va: size={$va->size()}\n";
+
+# ----- Set some values in the array -----
+
+# These operators copy the value of $a and $b to the vector array
+$va->set(0, $a);
+$va->set(1, $b);
+$va->set(2, addv($a, $b));
+
+# Get some values from the array
+
+print "Getting some array values\n";
+for ($i = 0; $i < 5; $i++) {
+    print "    va[$i] = {$va->get($i)->as_string()}\n";
+}
+
+?>