Provisional Rails 4 updates; specs pass

 - Mongoid 4 uses upstream bson lib enforcing serialization with $oid;
   we unwrap by monkey-patching like promiscous ( http://git.io/cDladA )
 - Rspec 3 deprecations quieted
Yes, Mongoid 3 used its own BSON library and now Mongoid 4is back to using the BSON library from 10gen: https://github.com/mongodb/bson-ruby/blob/master/lib/bson/object_id.rb#L74-L76