Support CTEs for UPDATE, DELETE, INSERT

[Former user]

Please support CTEs for DML statements.

Our application currently uses the attached code in our application to allow CTEs with DELETE, UPDATE, and INSERT. The code is pretty straightforward, and may give a hint on how to do this in the core code.

Thanks for looking at it,

Fred

[Former user]

Client code to activate CTEs for DELETE, INSERT, and UPDATE

[Mike Bayer]

this is #2551. its on the 0.9 track for now as 0.8 is overdue for beta releases.