Don't remove trailing slash from PATH_INFO for mounted apps

Previously when app was mounted as following:

    class Foo
      def call(env)
        [200, {}, [env['PATH_INFO']]]
      end
    end

    RackMountRailsBug::Application.routes.draw do
      mount RackTest.new => "/foo"
    end

trailing slash was removed from PATH_INFO. For example requesting

    GET /foo/bar/

on routes defined above would result in a response containing "/foo/bar"
instead of "/foo/bar/".

This commit fixes the issue.

(closes #3215)

actionpack/CHANGELOG.md

@@ -2,4 +2,8 @@
 
     *Piotr Sarnacki*, *Łukasz Strzałkowski*
 
+*   Fix removing trailing slash for mounted apps #3215
+
+    *Piotr Sarnacki*
+
 Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/actionpack/CHANGELOG.md) for previous changes.

actionpack/lib/action_dispatch/journey/router.rb

@@ -54,7 +54,7 @@ module ActionDispatch
       end
 
       def call(env)
-        env['PATH_INFO'] = Utils.normalize_path(env['PATH_INFO'])
+        env['PATH_INFO'] = normalize_path(env['PATH_INFO'])
 
         find_routes(env).each do |match, parameters, route|
           script_name, path_info, set_params = env.values_at('SCRIPT_NAME',
@@ -103,6 +103,12 @@ module ActionDispatch
 
       private
 
+        def normalize_path(path)
+          path = "/#{path}"
+          path.squeeze!('/')
+          path
+        end
+
         def partitioned_routes
           routes.partitioned_routes
         end

actionpack/test/dispatch/mount_test.rb

@@ -33,6 +33,11 @@ class TestRoutingMount < ActionDispatch::IntegrationTest
     Router
   end
 
+  def test_trailing_slash_is_not_removed_from_path_info
+    get "/sprockets/omg/"
+    assert_equal "/sprockets -- /omg/", response.body
+  end
+
   def test_mounting_sets_script_name
     get "/sprockets/omg"
     assert_equal "/sprockets -- /omg", response.body