Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

Conflicts:
	actionpack/lib/action_controller/metal/url_for.rb

- elmenth_path raise an ActiveResource::MissingPrefixParam exception when prefix_options does not has all required prefix_options ex: class StreetAddress < ActiveResource::Base self.site = "http://37s.sunrise.i:3000/people/:person_id/" end

    StreetAddress.element_path(1)
    # => ActiveResource::MissingPrefixParam

* for simple cases like User.last and User.order('name desc').last no need to perform Array#join operation.

* Instead of performing String#blank? do Array#empty?

* no need to create variable relation

Creating singleton class for every object whenever the instance-level accessor is used quite is expensive.