Turn on recursive with --summary

This makes "git log/diff --summary" imply recursive behaviour,
whose effect is summarized in one test output:

--- a/t/t4013/diff.diff-tree_--pretty_--root_--summary_initial
+++ b/t/t4013/diff.diff-tree_--pretty_--root_--summary_initial
@@ -5,7 +5,7 @@ Date: Mon Jun 26 00:00:00 2006 +0000

Initial

- create mode 040000 dir
+ create mode 100644 dir/sub
create mode 100644 file0
create mode 100644 file2
$

When a file is created in a subdirectory, we used to say just
the directory name only when that directory also was created,
which did not make sense from two reasons. It is not any more
significant to create a new file in a new directory than to
create a new file in an existing directory, and even if it were,
reportinging the new directory name without saying the actual
filename is not useful.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>