Add strict inequality check for Suit enumeration (#2687)

Fixes #2684

language/enumerations.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<!-- EN-Revision: 2e5f2910f3a2a95dcbdaf580ba57a0b60b072c2a Maintainer: pierrick Status: ready -->
+<!-- EN-Revision: 5744be5a4d239c18d4610581bd32b69a7d82947e Maintainer: lacatoire Status: ready -->
 <!-- Reviewed: no -->
  <chapter xml:id="language.enumerations" xmlns="http://docbook.org/ns/docbook">
   <title>Les énumérations</title>
@@ -106,6 +106,8 @@ $b = Suit::Spades;
 $a === $b; // true
 
 $a instanceof Suit;  // true
+
+$a !== 'Spades'; // true
 ?>
 ]]>
    </programlisting>