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>

diff.c

@@ -1741,6 +1741,7 @@ int diff_setup_done(struct diff_options *options)
 	 */
 	if (options->output_format & (DIFF_FORMAT_PATCH |
 				      DIFF_FORMAT_DIFFSTAT |
+				      DIFF_FORMAT_SUMMARY |
 				      DIFF_FORMAT_CHECKDIFF))
 		options->recursive = 1;
 	/*

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
 $