[PATCH] Parallelize the pull algorithm

[PATCH] Parallelize the pull algorithm

This processes objects in two simultaneous passes. Each object will
first be given to prefetch(), as soon as it is possible to tell that
it will be needed, and then will be given to fetch(), when it is the
next object that needs to be parsed. Unless an implementation does
something with prefetch(), this should have no effect.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>