Preserve RECURSIVE flag of CTE relations when they are merged.

[jsnelling]

This pull request fixes what I think to be a bug in the handling of recursive CTEs during merges.

Queries like the following:
Tag.all.merge(Tag.with.recursive(recursive: Tag.where(tag: 'tag')))
Tag.with.recursive(recursive: Tag.where(tag: 'tag')).merge(Tag.all)

would both be expected to produce a query like:
WITH RECURSIVE "recursive"
AS ( SELECT "tags".*
FROM "tags"
WHERE "tags"."tag" = 'tag')
SELECT "tags".*
FROM "tags"

but currently only the second one would. The first would lose the recursive flag
during merge and result in:
WITH "recursive"
AS ( SELECT "tags".*
FROM "tags"
WHERE "tags"."tag" = 'tag')
SELECT "tags".*
FROM "tags"

Adding :recursive to ActiveRecord::Relation::Merger#normal_values
and a #recursive! method to ActiveRecord::QueryMethods the expected behavior
regardless of the direction of the merge.

Closes # .

Changes proposed in this pull request

[edpaget]

Thank you @jsnelling I will review this weekend and hopefully merge

[jsnelling]

hey @edpaget, I wanted to check in and see if there was anything else that you needed from me on this PR?

[Papipo]

:(

[jsnelling]

@Papipo unfortunately, it doesn't seem that this project is active anymore