Add testing support for rails4.

* Closes #135
Add `needs_attr_accessible?` for ActiveRecord adapter.

* Based on plataformatec/devise#2515 avoid calling attr_accessible on Rails4, but do call it if it's defined on Rails3
Turn off deprecation warnings for testing on CI.

The volume of messages was causing Travis builds to error out.
Merge pull request #155 from assaf/feature/rails4

Add testing support for rails4