marked stl_concept_covering as an expected failure

[SVN r33975]

status/explicit-failures-markup.xml

@@ -348,6 +348,12 @@
                 <note author="B. Dawes" refid="3"/>
             </mark-failure>
         </test>
+        <test name="stl_concept_covering">
+            <mark-failure>
+                <toolset name="*"/>
+                <note author="Jeremy Siek" refid="1"/>
+            </mark-failure>
+        </test>
     </library>
 
     <!-- config -->