Fix bug: undefined method `select_all_column?' for []:ActiveRecord::Relation

If __ActiveRecord::Relation__ is load prior to __SecondLevelCache__, the
__SecondLevelCache::ActiveRecord::FinderMethods__ will only apply the methods
in included block, not all the methods including in the module.

The easiest solution is just to include the module to __ActiveRecord::Relation__
directly.

The way to run the test is

```ruby
rake test TEST=test/require_test.rb
```