Upgrade to Rails 4.0.0.beta:

This upgrades to Rails 4 at master and removes all the previous mass
assignment security code, updating to use ActiveModel's
ForbiddenAttributesProtection module.
Bump version
Remove Mongoid::Paranoia. [ close #2433 ]
Remove Mongoid::Versioning. [ close #2432 ]
Cleanup model tracking for index creation/deletion.
Remove multi parameter attributes
Fix the observers being removed from rails core
Cleanup more observer code. [ close #2597 ]
Boolean -> Mongoid::Boolean. [ fix #2648 ]
renaming db:reseed to db:reset
Update changelog
Namespace Railtie initializer and refactor.

[ fix #2659 ]
Fix broken railtie. [ fix #2659 ]
Exclude current failures
Bring back the detailed update selectors.

This is part 1 of #2545.
Remove the unused insert consumer
User $ operator where appropriate.

In the cases where the selector permits it, we now use the positional
operator on atomic updates for embedded documents nested at the first
level deep.

Documents lower than one level will continue to use indexes.

[ close #2545 ]
Update rdoc in atomic module
Dont' clone or dup 'id' fields. [ close #2704 ]