Update ruby-actionpack31 to 3.1.4.

Tweak COMMENT.

## Rails 3.1.4 (unreleased) ##

*  Skip assets group in Gemfile and all assets configurations options
    when the application is generated with --skip-sprockets option.

    *Guillermo Iguaran*

*  Use ProcessedAsset#pathname in Sprockets helpers when debugging is on.
    Closes #3333 #3348 #3361.

    *Guillermo Iguaran*

*  Allow to use asset_path on named_routes aliasing RailsHelper's
    asset_path to path_to_asset *Adrian Pike*

*  Assets should use the request protocol by default or default to relative
    if no request is available *Jonathan del Strother*

(taca)