This will make it easier to do various clever things that don't depend
on the pure tree contents. It also makes the parameter passing much
simpler - the callers doesn't really look at trees anywhere else, and
it's really the function that should look at the low-level details.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>