[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/overloading/runme.php

@@ -0,0 +1,58 @@
+<?php
+
+# This file illustrates the low-level C++ interface
+# created by SWIG.  In this case, all of our C++ classes
+# get converted into function calls.
+
+include("example.php");
+
+# ----- Object creation -----
+
+print "Creating some objects:\n";
+$c = new Circle(10);
+print "    Created circle \$c\n";
+$s = new Square(10);
+print "    Created square \$s\n";
+
+# ----- Access a static member -----
+
+print "\nA total of " . Shape::nshapes() . " shapes were created\n";
+
+# ----- Member data access -----
+
+# Set the location of the object.
+# Note: methods in the base class Shape are used since
+# x and y are defined there.
+
+$c->x = 20;
+$c->y = 30;
+$s->x = -10;
+$s->y = 5;
+
+print "\nHere is their current position:\n";
+print "    Circle = (" . $c->x . "," . $c->y . ")\n";
+print "    Square = (" . $s->x . "," . $s->y . ")\n";
+
+# ----- Call some methods -----
+
+print "\nCall some overloaded methods:\n";
+foreach (array(1, 2.1, "quick brown fox", $c, $s) as $o) {
+  print "        overloaded = " .  overloaded($o) . "\n";
+}
+
+# Need to unset($o) or else we hang on to a reference to the Square object.
+unset($o);
+
+# ----- Delete everything -----
+
+print "\nGuess I'll clean up now\n";
+
+# Note: this invokes the virtual destructor
+unset($c);
+$s = 42;
+
+print Shape::nshapes() . " shapes remain\n";
+
+print "Goodbye\n";
+
+?>