preserve CTE from a SELECT when doing INSERT...SELECT

[Mike Bayer]

related to #2551 but of lesser scope, if the select() passed to insert.from_select() has a cte() inside of it, we should render that inline:

    INSERT INTO data (id, data) WITH anon_1 AS
    (SELECT data2.id AS id, data2.data AS data
    FROM data2
    WHERE data2.data = 1)
     SELECT data2.id, data2.data
    FROM data2, anon_1
    WHERE data2.data = anon_1.data

PG supports the WITH both on top and under the INSERT, and they have different semantics: http://www.postgresql.org/docs/9.4/interactive/sql-insert.html "It is possible for the query (SELECT statement) to also contain a WITH clause. In such a case both sets of with_query can be referenced within the query, but the second one takes precedence since it is more closely nested.".

[Mike Bayer]

• Added official support for a CTE used by the SELECT present inside of :meth:.Insert.from_select. This behavior worked accidentally up until 0.9.9, when it no longer worked due to unrelated changes as part of 3248. Note that this is the rendering of the WITH clause after the INSERT, before the SELECT; the full functionality of CTEs rendered at the top level of INSERT, UPDATE, DELETE is a new feature targeted for a later release. fixes #3418

→ <<cset eb1bb84fbc10>>

[Mike Bayer]

• Added official support for a CTE used by the SELECT present inside of :meth:.Insert.from_select. This behavior worked accidentally up until 0.9.9, when it no longer worked due to unrelated changes as part of 3248. Note that this is the rendering of the WITH clause after the INSERT, before the SELECT; the full functionality of CTEs rendered at the top level of INSERT, UPDATE, DELETE is a new feature targeted for a later release. fixes #3418

(cherry picked from commit eb1bb84fbc10c801c7269a3d38c9e0235327857e)

→ <<cset 87c605e3dc8b>>