Change CPAN mirror again - metacpan is a complete backpan-backed mirror

This way the deletion of the usable version of Tree::DAG_Node won't
affect testing
EU::MM on < 5.8.9 got fixed
Check that each preinstall on an old CPAN.pm completes
Only run our own tests concurrently, not stuff in after_success
Reorder travis tests by length, add 5.12.4
Make sure we can load each DBICTest::Schema result individually

This will ensure tests always fail if some sort of circular load order
issue is encountered, and we won't have to wait for a particular random
loading sequence to blow up the tests
Rename internal rsrc method to be more descriptive, stop proxying it
Excise unreachable code