Suppport prepared statements features

- prepared statements can be disabled
https://github.com/rails/rails/commit/fd398475afb64e362059a500e5cd54d08b9afdee
- Created block to by-pass the prepared statement bindings.
https://github.com/rails/rails/commit/9f549212c3b6c8ae4684da61e03a04da9f341fad
Merge pull request #295 from yahonda/unprepared_visitor

Suppport prepared statements features
Use the index name explicitly provided in a migration when reverting

see rails/rails#8868
Merge pull request #296 from yahonda/rails8868

Use the index name explicitly provided in a migration when reverting
Deprecate #connection in favour of accessing it via the class

see rails/rails#9371
Merge pull request #297 from yahonda/deprecate_connection

Deprecate #connection in favour of accessing it via the class