[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/simple/runme.php

@@ -0,0 +1,25 @@
+<?php
+
+require "example.php";
+
+# Call our gcd() function
+
+$x = "42 aaa";
+$y = 105;
+$g = gcd($x,$y);
+print "The gcd of $x and $y is $g\n";
+
+# Manipulate the Foo global variable
+
+# Output its current value
+print "Foo = " . Foo_get() . "\n";
+
+# Change its value
+Foo_set(3.1415926);
+
+# See if the change took effect ( this isn't a good example for php, see
+#				  manual for why. )
+print "Foo = "  . Foo_get() . "\n";
+print_Foo();
+
+?>