files in the lib directory are no longer autoloaded

Conceptually, the lib directory is closer 3rd party libraries
than to the application itself. Thus, Rails adds it to Ruby's
load path ($LOAD_PATH, $:) but it is no longer included in
dependencies' load paths.

To enable autoloading back put this in your config/application.rb

  config.load_paths += %W( #{config.root}/lib )

railties/lib/rails/engine/configuration.rb

@@ -20,15 +20,19 @@ module Rails
           paths.app.models          "app/models",          :eager_load => true
           paths.app.mailers         "app/mailers",         :eager_load => true
           paths.app.views           "app/views"
-          paths.lib                 "lib",                 :load_path => true
+
+          paths.lib                 "lib"
           paths.lib.tasks           "lib/tasks",           :glob => "**/*.rake"
+
           paths.config              "config"
           paths.config.initializers "config/initializers", :glob => "**/*.rb"
           paths.config.locales      "config/locales",      :glob => "*.{rb,yml}"
           paths.config.routes       "config/routes.rb"
+
           paths.public              "public"
           paths.public.javascripts  "public/javascripts"
           paths.public.stylesheets  "public/stylesheets"
+
           paths
         end
       end

railties/test/application/initializers/load_path_test.rb

@@ -19,7 +19,7 @@ module ApplicationTests
       assert $:.include?("#{app_path}/app/models")
     end
 
-    test "initializing an application allows to load code on lib path inside application class definitation" do
+    test "initializing an application allows to load code on lib path inside application class definition" do
       app_file "lib/foo.rb", <<-RUBY
         module Foo; end
       RUBY
@@ -60,6 +60,8 @@ module ApplicationTests
 
       add_to_config <<-RUBY
         config.root = "#{app_path}"
+        config.cache_classes = true
+        config.load_paths << "#{app_path}/lib"
         config.eager_load_paths << "#{app_path}/lib"
       RUBY