Add 'import testing'.

This is necessary so that things work when Boost.Serialization Jamfiles
directly depend on some of the config tests.


[SVN r43985]

libs/config

@@ -1 +1 @@
-Subproject commit da6e707602081e45eafe5378436c9b581d279f71
+Subproject commit 6f2afd458cdc39bd5eb46ba00d9d45a8308f1cea