diff: plug leaks in dirstat

The array of dirstat_file contained in the dirstat_dir structure is
not freed after the processing ends.  Unfortunately, the member that
points at the array, .files, is incremented as the gather_dirstat()
function recursively walks it, and this needs to be plugged by
remembering the beginning of the array before gather_dirstat() mucks
with it and freeing it after we are done.

We can mark t4047 as leak-free.  t4000, which is marked as
leak-free, now can exercise dirstat in it, which will happen next.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -2975,13 +2975,18 @@ static void conclude_dirstat(struct diff_options *options,
 			     struct dirstat_dir *dir,
 			     unsigned long changed)
 {
-	/* This can happen even with many files, if everything was renames */
-	if (!changed)
-		return;
+	struct dirstat_file *to_free = dir->files;
 
-	/* Show all directories with more than x% of the changes */
-	QSORT(dir->files, dir->nr, dirstat_compare);
-	gather_dirstat(options, dir, changed, "", 0);
+	if (!changed) {
+		/* This can happen even with many files, if everything was renames */
+		;
+	} else {
+		/* Show all directories with more than x% of the changes */
+		QSORT(dir->files, dir->nr, dirstat_compare);
+		gather_dirstat(options, dir, changed, "", 0);
+	}
+
+	free(to_free);
 }
 
 static void show_dirstat(struct diff_options *options)

t/t4047-diff-dirstat.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='diff --dirstat tests'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # set up two commits where the second commit has these files