move cache_digests rake methods into their own namespace

[modosc]

we found a bug when running this task in our CI system:

RAILS_ENV="test" RACK_ENV="test" bundle exec rake db:create db:schema:load --trace

actionview/lib/action_view/tasks/dependencies.rake defines two methods that end up in the global namespace, and these shadowed an attribute with the same name (template_name) in a FactoryGirl factory:

FactoryGirl.define do
  factory :foo do
    template_name "blah"
  end
end

which resulted in this error:

ArgumentError: wrong number of arguments (1 for 0)
.../gems/actionview-4.1.6/lib/action_view/tasks/dependencies.rake:14:in `template_name'
.../spec/factories/foo.rb:3:in `block (2 levels) in <top (required)>'

to resolve i just stuck these in their own namespace but you might consider having a namespace just for rake first (RakeHelpers or something) and then putting this class inside that one. i'm guessing this isn't the only place where the global namespace is being polluted from a rake task.

[chollier]

I had the exact same issue