testing swap() in a separate file

test/Jamfile.v2

@@ -17,6 +17,7 @@ import testing ;
 {
   test-suite optional :
     [ run optional_test.cpp ]
+    [ run optional_test_swap.cpp ]
     [ run optional_test_conversions_from_U.cpp ]
     [ run optional_test_tie.cpp ]
     [ run optional_test_ref_assign_portable_minimum.cpp ]