remote-curl: Refactor walker initialization We will need the walker, url and remote in other functions as the code grows larger to support smart HTTP. Extract this out into a set of globals we can easily reference once configured. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> CC: Daniel Barkalow <barkalow@iabervon.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>