diff-tree -r -t: include added/removed directories in the output

diff-tree -r -t: include added/removed directories in the output

We used to include only the modified and typechanged directories
in the ouptut, but for consistency's sake, we should also include
added and removed ones as well.

This makes the output more consistent, but it may break existing scripts
that expect to see the current output which has long been the established
behaviour.

Signed-off-by: Nick Edelen <sirnot@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>