Don't hardcode assets route skipped in route inspector

[guilleiguaran]

Right now generating a resource named asset with scaffold and setting config.assets.prefix = '/sprockets' (to avoid conflicting with generated resources) the output of rake routes is:

/tmp/foo % rake routes
  /sprockets #<Sprockets::Environment:0x3fea8846578c root="/private/tmp/foo", paths=["/private/tmp/foo/app/assets/images", "/private/tmp/foo/app/assets/javascripts", "/private/tmp/foo/app/assets/stylesheets", "/private/tmp/foo/vendor/assets/javascripts", "/private/tmp/foo/vendor/assets/stylesheets", "/Users/guille/.rbenv/versions/1.9.3-p0/lib/ruby/gems/1.9.1/gems/jquery-rails-2.0.0/vendor/assets/javascripts", "/Users/guille/.rbenv/versions/1.9.3-p0/lib/ruby/gems/1.9.1/bundler/gems/coffee-rails-6b4034abbf7d/lib/assets/javascripts"], digest="aa7d0db7619379e13b08335dee027df2">

This have two issues, the first one is that any of the routes prefixed with /assets is shown and the second one is that the /sprockets one shouldn't be shown.

After of apply this patch, the output rake routes is the expected:

/tmp/foo % rake routes
    assets GET    /assets(.:format)          assets#index
           POST   /assets(.:format)          assets#create
 new_asset GET    /assets/new(.:format)      assets#new
edit_asset GET    /assets/:id/edit(.:format) assets#edit
     asset GET    /assets/:id(.:format)      assets#show
           PUT    /assets/:id(.:format)      assets#update
           DELETE /assets/:id(.:format)      assets#destroy

[josevalim]

For 3-2-stable as well pls?