Test against multiple Active Record versions on Travis CI
Don't run Active Record 4.0.0.beta1 against Ruby 1.8.x on Travis CI

Also, allow failures for 4.0.0.beta1 for now.
Stop supporting Active Record 3.0
Active Record has a space in its name
Stop checking for ActiveRecord::Relation

We only support Active Record 3.1 or higher, so no need for this check
anymore.
Support sanitize_sql_array in Active Record 3.1

The goal is to stop calling sanitize_sql_array soon, though.