ant target resolve-default to keep test libs

The ant target resolve-default depends on clean-lib which causes all libs to be removed, including test libs which are then not resolved again. After

% ant resolve-test resolve-default

build/test/lib/ is missing. Also any targets which depend on resolve-default can cause the libs to disappear. There is no impact on the build as such but Eclipse does complain if libs are missing (eg. junit) and there is no fast way to let them re-appear (except running target "test" which takes long).