[Feature Request] Pull request: Support custom protocol in options passed to asset_url


That pull allows specifying e.g. protocol: :relative when calling the asset_url helper, instead of always using the request protocol.

This is useful if, for example, you have a fragment that is served over both http and https and you want to use a relative protocol so the same cache can be used in both cases.

(Not sure if it’s necessary to send this to the mailing list too, but the contributing guide seems to say it is.)