[wwwdocs] update gcc-4.7/changes.html

[Jonathan Wakely]

Add note on thread improvements to libstdc++ changes.

Committed to cvs.

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.7/changes.html,v
retrieving revision 1.75
diff -u -r1.75 changes.html
--- changes.html        5 Feb 2012 15:11:23 -0000       1.75
+++ changes.html        8 Feb 2012 00:42:40 -0000
@@ -412,6 +412,7 @@
          <li> uses-allocator construction for <code>tuple</code>; </li>
          <li> <code>vector</code> meets the allocator-aware container 
requirements; </li>
          <li> replacing <code>monotonic_clock</code> with 
<code>steady_clock</code>; </li>
+         <li> enabling the thread support library on a wider range of targets; 
</li>
          <li> many small improvements to conform to the FDIS. </li>
        </ul>
      </li>