umask does not play well with windows.

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@33235 c90b9560-bf6c-de11-be94-00142212c4b1

functions/filesystem.xml

@@ -2486,6 +2486,11 @@ if (touch ($FileName)) {
      <function>Umask</function> without arguments simply returns the
      current umask.
     </para>
+    <note>
+     <simpara>
+      This function may not work on Windows systems.
+     </simpara>
+    </note>
    </refsect1>
   </refentry>