doc patch to fix libstdc++/51701

[Jonathan Wakely]

        PR libstdc++/51701
        * doc/xml/manual/extensions.xml (Input and Output): Remove reference
        to RWLock class.

Committed to trunk.
-------------- next part --------------
Index: doc/xml/manual/extensions.xml
===================================================================
--- doc/xml/manual/extensions.xml	(revision 182661)
+++ doc/xml/manual/extensions.xml	(working copy)
@@ -475,14 +475,7 @@ get_temporary_buffer(5, (int*)0);
 	 descriptor, and provides the <code>fd()</code> function.
      </para></listitem>
    </itemizedlist>
-   <para>If you want to access a <code>filebuf</code>'s file descriptor to
-      implement file locking (e.g. using the <code>fcntl()</code> system
-      call) then you might be interested in Henry Suter's RWLock class.
-      <!-- url="http://suter.home.cern.ch/suter/RWLock.html" -->
-   </para>
 
-    <para>
-    </para>
   </section>
 </chapter>