- [bug] further tweak to the fix from [ticket:2261],

- [bug] further tweak to the fix from [ticket:2261],
so that generative methods work a bit better
off of cloned (this is almost a non-use case though).
In particular this allows with_only_columns()
to behave more consistently.   Added additional
documentation to with_only_columns() to clarify
expected behavior, which changed as a result
of [ticket:2261].  [ticket:2319]
- document the crap out of with_only_columns, include caveats about
the change, etc.