t4013: test "git diff-tree -m"

We want to ensure we don't affect plumbing commands with our changes
of "-m" semantics, so add corresponding test.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4013-diff-various.sh

@@ -293,6 +293,7 @@ diff-tree --stat initial mode
 diff-tree --summary initial mode
 
 diff-tree master
+diff-tree -m master
 diff-tree -p master
 diff-tree -p -m master
 diff-tree -c master