Fix arity problem with rails 4.1.0

Fix specs for airty check

Don't check arity, just check the AR version
Clean with truncation at the start of each suite.

This keeps things working properly for mongo which does not support
transactions. The strategy is still properly configured to use
transactions where supported, though, so this should not affect
the speed of the test suite for other ORMs.
Fix for Model.all.page in DataMapper
Restoring global configuration value.

Without setting this back to nil, this affects all other tests.
Removed invalid test.

No other ORM tests for `current_page` to work on the model, and there
is no documentation that indicates that this should work this way. I
believe this test was added accidentally.
Fixed tests targeting Rails ~> 4.0.0.
Tests targeting Rails < 4.1 rather than ~> 4.0.0
Testing that `paginate` helper properly works under mouted Engine
Revert "Rails 3.0.x fails to load helpers in Engines (?)"

This reverts commit 00c912d12bc49c0e7b3d748854e0bdce94ff3470.

reason: reverting back from app/helpers to ActionView::Base freedom-patch.
Because mounted engines on the app doesn't search the main_app's helpers, then throws "undefined method `paginate'" in the views
Revert "An Engine can include app/helpers, so let's move the helpers there"

This reverts commit 2ed8adfe378594ae1585ac4a457a6d01f04478eb.

reason: Because mounted engines on the app doesn't search the main_app's helpers, then throws "undefined method `paginate'" in the views
:scissors:
Get rdoc working correctly
Merge branch 'pass-test-suite' of github.com:wbyoung/kaminari into wbyoung-pass-test-suite

Conflicts:
	spec/models/active_record/active_record_relation_methods_spec.rb
Merge branch 'pass-test-suite' of github.com:wbyoung/kaminari

Conflicts:
	spec/models/active_record/active_record_relation_methods_spec.rb
Merge branch 'wbyoung-pass-test-suite'