Somewhere in the process of finishing up builtin-clone, the update of
the working tree was lost. This was due to not using the option "merge"
for unpack_trees().
Breakage noticed by Kevin Ballard.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Tested-by: Jeff King <peff@peff.net> Acked-by: Daniel Barkalow <barkalow@iabervon.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>