there's no need to "use blib", since we know where the libraries are

this might avoid the random failures we see with t/usecase_list8
improve subtest_load to test loading a theme in isolation

this will detect subtle bugs related to loading order, like:

    use Acme::MetaSyntactic::List;
    our @ISA = qw( Acme::MetaSyntactic::MultiList );

where the parent class is in fact not loaded