Marked up VC6/7 as unusable with TR1.

[SVN r34412]

status/explicit-failures-markup.xml

@@ -3929,10 +3929,13 @@ for more information.
     <library name="tr1">
         <mark-unusable>
             <toolset name="msvc"/>
+            <toolset name="vc-7.0"/>
+            <toolset name="msvc-7.0"/>
+            <toolset name="msvc-6*"/>
             <toolset name="VC6*"/>
             <toolset name="vc-6*"/>
             <note author="John Maddock">
-                VC6 has a buggy using declaration syntax which
+                VC6/7 has a buggy using declaration syntax which
                 basically makes it impossible to implement the 
                 namespace forwarding that this library relies upon.
                 See KB article 263630 here: http://support.microsoft.com/default.aspx?scid=kb;en-us;263630