Add a test that demonstrates the problem.
The outer side of a group join needs to be included in the Flatten always, since it makes more rows appear with nulls.
merge MMcM: An outer join parent must be included in flatten, even if no table columns are used anywhere

Merge pull request #1235 from MMcM/sql-layer/sql-outer-must-join
https://github.com/FoundationDB/sql-layer/pull/1235