make the previous optimization work also on path-limited rev-list --bisect
make the previous optimization work also on path-limited rev-list --bisect

The trick is to give a child commit that is not tree-changing
the same depth as its parent, so that the depth is propagated
properly along strand of pearls.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git