Exception Notifiable should not override rescue_action_in_public

In its actual implementation, Exception Notifiable overrides
rescue_action_in_public. So if the user overrides it also, or the user
implementation or the plugin won't work.

The solution is use alias_method_chain.

Ticket with patch here:

http://rails.lighthouseapp.com/projects/8995-rails-plugins/tickets/16-exception-notifiable-should-not-override-rescue_action_in_public