Fixed buggy jamfile.

When building from top-level boost-book build, incorrect path to
header files was corrupting the whole build.


[SVN r23566]

doc/Jamfile.v2

@@ -2,8 +2,8 @@ project boost-sandbox/utility/doc ;
 import boostbook ;
 import doxygen ;
 
-doxygen reference : ../../../boost/logic/tribool.hpp 
-                    ../../../boost/logic/tribool_fwd.hpp 
-                    ../../../boost/logic/tribool_io.hpp 
+doxygen reference : [ glob ../../../boost/logic/tribool.hpp ]
+                    [ glob ../../../boost/logic/tribool_fwd.hpp ]
+                    [ glob ../../../boost/logic/tribool_io.hpp ]
                   ;
 boostbook tribool : tribool.boostbook ;