Updated tests and jamfiles to reflect the changed testing headers location.

test/back.cpp

@@ -13,7 +13,7 @@
 
 #include <boost/mpl/back.hpp>
 #include <boost/mpl/range_c.hpp>
-#include <boost/mpl/aux_/test.hpp>
+#include "test.hpp"
 
 template< typename Seq, int value > struct back_test
 {