remote-helpers: Support custom transport options Some transports, like the native pack transport implemented by fetch-pack, support useful features like depth or include tags. These should be exposed if the underlying helper knows how to use them. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> CC: Daniel Barkalow <barkalow@iabervon.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>