Fix arity problem with rails 4.1.0

Fix specs for airty check

Don't check arity, just check the AR version
Add minitest to AR edge
This gets Mongo and DataMapper specs running
but newer versions of AR, and incidentally Sinatra specs still fail.
Use database_cleaner ~> 1.2.0 for tests
use kaminari.gemspec database_cleaner in sub gemfiles
Use truncation for DataMapper
lock mongoid_30 at ~> 3.0.0
test against mongoid ~> 3.1.0 with rails ~> 4.0.0
allow some failures :trollface:
allow failures on travis for sinatra_13 and sinatra_14

based on a patch by @wbyoung #451
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
Merge pull request #449 from bricker/count-arity

Arity on #count with rails 4.1.0
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