Fix copy-pasted comments related to tree diff handling.

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

diff.c

diff --git a/diff.c b/diff.c
index 0e2e872..340d878 100644
--- a/diff.c
+++ b/diff.c
@@ -3527,7 +3527,7 @@
 
 	if ((DIFF_FILE_VALID(p->one) && S_ISDIR(p->one->mode)) ||
 	    (DIFF_FILE_VALID(p->two) && S_ISDIR(p->two->mode)))
-		return; /* no tree diffs in patch format */
+		return; /* no useful stat for tree diffs */
 
 	run_diffstat(p, o, diffstat);
 }
@@ -3540,7 +3540,7 @@
 
 	if ((DIFF_FILE_VALID(p->one) && S_ISDIR(p->one->mode)) ||
 	    (DIFF_FILE_VALID(p->two) && S_ISDIR(p->two->mode)))
-		return; /* no tree diffs in patch format */
+		return; /* nothing to check in tree diffs */
 
 	run_checkdiff(p, o);
 }