Drop toplevel app/assets load path.

Bump version to 3.0.0.beta3

`app/assets` was added to give `manifest.js` a place to live, but it
suggests that `require 'stylesheets/foo.css'` might be the right way to
refer to `require 'foo.css'`.

We resolve the overlap and clarify that `manifest.js` is config by
moving it from `app/assets/` to `app/assets/config/`. Put it up on a
pedestal: rails/rails#21794

This reverts #232 and commit 39ecb27,
reversing changes made to 3a44d47.

Author: jeremy

lib/sprockets/rails/version.rb

@@ -1,5 +1,5 @@
 module Sprockets
   module Rails
-    VERSION = "3.0.0.beta2"
+    VERSION = "3.0.0.beta3"
   end
 end

lib/sprockets/railtie.rb

@@ -47,7 +47,6 @@ class Engine < Railtie
       initializer :append_assets_path, :group => :all do |app|
         app.config.assets.paths.unshift(*paths["vendor/assets"].existent_directories)
         app.config.assets.paths.unshift(*paths["lib/assets"].existent_directories)
-        app.config.assets.paths.unshift(*paths["app"].existent_directories.grep(/\/assets\z/))
         app.config.assets.paths.unshift(*paths["app/assets"].existent_directories)
       end
     end