Update lib/tire/model/search.rb

Dont use @attrributes hash
revert multi_json update for Rails 3.1
use _format for the type and id as _id
warning note on the lack tire compatability

TODO: extract the dsl into gds search client and use that instead
Merge pull request #1 from alphagov/rummager

For use with Rummager & Whitehall