Merged requested to merge require-upgrade-tests into master
The original upgrade tests were disabled by default for being too slow. They're too slow because they test with a wide range of previous ASDF versions.
Add new tests that run only if the full upgrade test suite is not run. These test upgrading only from the implementation provided ASDF. This is much faster than testing every old version. Plus, it matches the real world upgrade conditions for the vast majority of users.
This catches #72 (closed).