Fix documentation build error.

Author: stefanseefeld

doc/numpy/_templates/layout.html

@@ -90,7 +90,7 @@
       <tr>
         <td valign="top" width="300">
           <h3><a href="{{ pathto('index') }}"><img 
-          alt="C++ Boost" src="{{ pathto('_static/' + logo, 1) }}" border="0"></a></h3>
+          alt="C++ Boost" src="{{ pathto('_static/bpl.png', 1) }}" border="0"></a></h3>
         </td>
 
         <td >