Do only follow HTTP and HTTPS redirects

We do not want to follow redirects to other protocols since they might allow an adversary to bypass network restrictions. (i.e. a redirect to ftp:// might be used to access files of a FTP server which might be in a secure zone and not be reachable from the net but from the ownCloud server)
Are you sure this is correct? The manual says `resource stream_context_create ([ array $options [, array $params ]] )` and the previous patch had null as the first parameter.