[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/swig_exception_runme.php

@@ -0,0 +1,33 @@
+<?php
+
+require("swig_exception.php");
+require("tests.php");
+
+$c = new Circle(10);
+$s = new Square(10);
+
+if (Shape::nshapes() != 2) {
+    check::fail("Shape::nshapes() should be 2, actually ".Shape::nshapes());
+}
+
+# ----- Throw exception -----
+try {
+    $c->throwException();
+    check::fail("Exception wasn't thrown");
+} catch (Exception $e) {
+    if ($e->getMessage() != "OK") {
+	check::fail("Exception getMessage() should be \"OK\", actually \"".$e->getMessage()."\"");
+    }
+}
+
+# ----- Delete everything -----
+
+$c = NULL;
+$s = NULL;
+$e = NULL;
+
+if (Shape::nshapes() != 0) {
+    check::fail("Shape::nshapes() should be 0, actually ".Shape::nshapes());
+}
+
+?>