Fix sorting of helpers from different paths

When more than one directory for helpers is provided to a controller, it
should preserver the order of directories. Given 2 paths:

    MyController.helpers_paths = ["dir1/helpers", "dir2/helpers"]

helpers from dir1 should be loaded first. Before this commit, all
helpers were mixed and then sorted alphabetically, which essentially
would require to rename helpers to get desired order.

This is a problem especially for engines, where you would like to be
able to predict accurately which engine helpers will load first.

actionpack/lib/action_controller/metal/helpers.rb

@@ -96,9 +96,9 @@ def all_helpers_from_path(path)
         helpers = []
         Array.wrap(path).each do |_path|
           extract  = /^#{Regexp.quote(_path.to_s)}\/?(.*)_helper.rb$/
-          helpers += Dir["#{_path}/**/*_helper.rb"].map { |file| file.sub(extract, '\1') }
+          names = Dir["#{_path}/**/*_helper.rb"].map { |file| file.sub(extract, '\1') }
+          helpers += names.sort
         end
-        helpers.sort!
         helpers.uniq!
         helpers
       end

actionpack/test/controller/helper_test.rb

@@ -50,12 +50,42 @@ def lib
 class MeTooController < JustMeController
 end
 
+class HelpersPathsController < ActionController::Base
+  paths = ["helpers1_pack", "helpers2_pack"].map do |path|
+    File.join(File.expand_path('../../fixtures', __FILE__), path)
+  end
+  $:.unshift(*paths)
+
+  self.helpers_path = paths
+  helper :all
+
+  def index
+    render :inline => "<%= conflicting_helper %>"
+  end
+end
+
 module LocalAbcHelper
   def a() end
   def b() end
   def c() end
 end
 
+class HelperPathsTest < ActiveSupport::TestCase
+  def setup
+    @request    = ActionController::TestRequest.new
+    @response   = ActionController::TestResponse.new
+  end
+
+  def test_helpers_paths_priority
+    request  = ActionController::TestRequest.new
+    responses = HelpersPathsController.action(:index).call(request.env)
+
+    # helpers2_pack was given as a second path, so pack2_helper should be
+    # included as the second one
+    assert_equal "pack2", responses.last.body
+  end
+end
+
 class HelperTest < ActiveSupport::TestCase
   class TestController < ActionController::Base
     attr_accessor :delegate_attr

actionpack/test/fixtures/helpers1_pack/pack1_helper.rb

@@ -0,0 +1,5 @@
+module Pack1Helper
+  def conflicting_helper
+    "pack1"
+  end
+end

actionpack/test/fixtures/helpers2_pack/pack2_helper.rb

@@ -0,0 +1,5 @@
+module Pack2Helper
+  def conflicting_helper
+    "pack2"
+  end
+end