Ensure loading of models in rake tasks, to allow for threadsafe execu…

…tion. Fixes #1236.

lib/mongoid/railtie.rb

@@ -95,7 +95,14 @@ def self.generator
      # environments.
      initializer "preload all application models" do |app|
        config.to_prepare do
          ::Rails::Mongoid.preload_models(app) unless $rails_rake_task
          if $rails_rake_task
            # We previously got rid of this, however in the case where
            # threadsafe! is enabled we must load all models so things like
            # creating indexes works properly.
            ::Rails::Mongoid.load_models(app)
          else
            ::Rails::Mongoid.preload_models(app)
          end
        end
      end