Don't pluralize collection named routes twice.

In english, usually pluralizing a word twice gives the same result as pluralizing it just once.

However, with some words, and in many foreign languages, this is not the case.

For example, the plural of "taxi" is "taxis", but the plural of "taxis" is "taxes". We were pluralizing the resource :taxis, so were generating "taxes_path" instead of "taxis_path".

It affected applications using custom inflection rules, such as spanish ones.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -511,7 +511,7 @@ def member_name
 
           # Checks for uncountable plurals, and appends "_index" if they're.
           def collection_name
-            singular == plural ? "#{plural}_index" : plural
+            singular == plural ? "#{name}_index" : name
           end
 
           def resource_scope

actionpack/test/dispatch/routing_test.rb

@@ -188,6 +188,7 @@ def self.matches?(request)
       end
 
       resources :sheep
+      resources :taxis
 
       resources :clients do
         namespace :google do
@@ -965,6 +966,14 @@ def test_resources_for_uncountable_names
       assert_equal '/sheep/1/edit', edit_sheep_path(1)
     end
   end
+
+  def test_named_paths_for_resources_with_irregular_plural_of_the_plural
+    with_test_routes do
+      assert_equal '/taxis/1', taxi_path(1)
+      assert_equal '/taxis', taxis_path
+      assert_raise(NameError) { taxes_path }
+    end
+  end
 
   def test_path_names
     with_test_routes do