Delegate indexed_name to setup of the joined model class

[heaven]

This should be way more reliable than trying to guess the name, which can hardly work if the original field was configured with the :as option.

[serggl]

is there away to have a spec for this? it's kind of hard to understand the changes made here

[heaven]

The change is that previously I tried to build the indexed_name for joined fields like this was done for regular fields, which didn't work well in case when the field from the joined model was defined with :as option.

Example:

class User < ActiveRecord::Base
  has_one :profile

  searchable do
    join(:name,
      :prefix => :profile,
      :target => 'Profile',
      :type => :text,
      :join => { :from => :member_id, :to => :id })
  end
end

class Profile < ActiveRecord::Base
  belongs_to :user

  searchable do
    text :name, :as => :name_custom_ngram_filter_factory
  end
end

Previously, when searching User by profile_name field Sunspot would try using the name_text field name while it should be name_custom_ngram_filter_factory.

Since we don't know all the options original field was created with when defining joined fields, it's easier to find an already configured field in Profile's setup and get the indexed_name from it.

I'll take a look at the test, probably I can add additional scenarios, like the one described above.