added a visitor for Set objects
Wrap nested Nodes::Grouping in brackets only once
Fix lt & lteq don't accept most of values.
Add SelectManager#distinct_on to set/unset Arel::Nodes::DistinctOn quantifier
Change specs to cover lt, lteq, gt and gteq.
Merge pull request #277 from sergey-alekseev/wrap-nested-gropings-only-once

Wrap nested Nodes::Grouping in brackets only once
Merge pull request #304 from bigxiang/fix_lt_and_lteq_error

Fix lt & lteq don't accept most of values.
Merge pull request #306 from mxhold/master

Add SelectManager#distinct_on to set/unset Arel::Nodes::DistinctOn quantifier
`Extract#as` should not mutate the receiver

Fixes https://github.com/rails/rails/issues/16913
Merge pull request #311 from tamird/master

`Extract#as` should not mutate the receiver
Wrap group_by sql with a subquery for limiting rows in Oracle.

Fixes #128
Merge pull request #315 from tamird/129

Wrap group_by sql with a subquery for limiting rows in Oracle.
Build on ruby-head
Remove unused @alias, being referenced in hashing.
Merge pull request #316 from vipulnsward/remove-alias

Remove unused @alias, being referenced in hashing.
Informix versions < 10 use 'FIRST' keyword instead of 'LIMIT'
Still supported in versions 10+
Merge pull request #137 from dimko/visit_set

Added a visitor for Set objects
Merge pull request #167 from pparidans/informix-v9-support

Informix versions < 10 use 'FIRST' keyword instead of 'LIMIT'
Fix set visiting spec
Merge pull request #317 from dimko/patch-2

Fix set visiting spec