Record flattening for all queries

[jamescheney]

It is straightforward (at least conceptually) to allow nested records in query results for any of the current query policies: the shredding/nested query code contains a transformation to do this so-called record flattening, but it is not currently performed for the other query policies. This would avoid the current dependency of temporal queries on query nested, and perhaps make it easier to use ordering (which is supported only by query flat; but I have no idea whether just composing things would be sensible w.r.t. the temporal query code, so more work might be needed there.)