This introduces a join_types field for equeries, which helps

instrument join types (such as INNER vs. OUTER JOINs). That can be

useful in ensuring that queries are joining in a way that the developers

expect, which can have an impact on results.
This is off by default, for compatibility. If a mismatch would have been

reported, then a warning will be issued advising the developer to opt in

and that it will be made the default in a future version.
There's also a fix for formatting sets, ensuring they're both sorted

and pretty-printed.

Unit tests pass.
Made use of this in some in-progress tests.