the output from the command omits entries that match the
<branch1> tree.
But currently "added in branch1" and "removed in branch1" (both while
unchanged in branch2) do print output. Change this so that the
behaviour matches the documentation.
Signed-off-by: John Keeping <john@keeping.me.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>