Don't send identity header if we want to do gzip compression

Don't send identity header if we want to do gzip compression

Propfind replies send 'Content-encoding: identity' right now, which is superseeded by the frameworks 'Content-encoding: gzip' in case of the client indicates this.
sending that headers twice has uncertain results depending on the client; while the RFC demands to evaluate the later, some fail to read our reply then.