Support non-protocol URLs that start with //

[rhukster]

Some non http/https CDNs use protocol-less URLs that are not ignored by the current regex.

Workaround at the moment is to use ?nocdn on the URL to disable CDN matching.

[mahagr]

Did you mean to close this one?

Likely needs the same fix for url() function as:
gantry/gantry5#469