Fix '--dirstat' with cross-directory renaming

The dirstat code depends on the fact that we always generate diffs with
the names sorted, since it then just does a single-pass walk-over of the
sorted list of names and how many changes there were. The sorting means
that all files are nicely grouped by directory.

That all works fine.

Except when we have rename detection, and suddenly the nicely sorted list
of pathnames isn't all that sorted at all. And now the single-pass dirstat
walk gets all confused, and you can get results like this:

  [torvalds@nehalem linux]$ git diff --dirstat=2 -M v2.6.27-rc4..v2.6.27-rc5
     3.0% arch/powerpc/configs/
     6.8% arch/arm/configs/
     2.7% arch/powerpc/configs/
     4.2% arch/arm/configs/
     5.6% arch/powerpc/configs/
     8.4% arch/arm/configs/
     5.5% arch/powerpc/configs/
    23.3% arch/arm/configs/
     8.6% arch/powerpc/configs/
     4.0% arch/
     4.4% drivers/usb/musb/
     4.0% drivers/watchdog/
     7.6% drivers/
     3.5% fs/

The trivial fix is to add a sorting pass, fixing it to:

  [torvalds@nehalem linux]$ git diff --dirstat=2 -M v2.6.27-rc4..v2.6.27-rc5
    43.0% arch/arm/configs/
    25.5% arch/powerpc/configs/
     5.3% arch/
     4.4% drivers/usb/musb/
     4.0% drivers/watchdog/
     7.6% drivers/
     3.5% fs/

Spot the difference. In case anybody wonders: it's because of a ton of
renames from {include/asm-blackfin => arch/blackfin/include/asm} that just
totally messed up the file ordering in between arch/arm and arch/powerpc.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -1054,6 +1054,13 @@ static long gather_dirstat(FILE *file, struct dirstat_dir *dir, unsigned long ch
 	return this_dir;
 }
 
+static int dirstat_compare(const void *_a, const void *_b)
+{
+	const struct dirstat_file *a = _a;
+	const struct dirstat_file *b = _b;
+	return strcmp(a->name, b->name);
+}
+
 static void show_dirstat(struct diff_options *options)
 {
 	int i;
@@ -1113,6 +1120,7 @@ static void show_dirstat(struct diff_options *options)
 		return;
 
 	/* Show all directories with more than x% of the changes */
+	qsort(dir.files, dir.nr, sizeof(dir.files[0]), dirstat_compare);
 	gather_dirstat(options->file, &dir, changed, "", 0);
 }