to_string adjustments

[SVN r44192]

test/Jamfile.v2

@@ -9,6 +9,7 @@ import testing ;
 
 #to_string
 run is_output_streamable_test.cpp ;
+run has_to_string_test.cpp ;
 run to_string_test.cpp ;
 run to_string_stub_test.cpp ;
 compile-fail to_string_fail.cpp ;