rerere: make sorting really stable.

The earlier code does not swap hunks when the beginning of the
first side is identical to the whole of the second side.  In
such a case, the first one should sort later.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

builtin-rerere.c

@@ -117,10 +117,13 @@ static int handle_file(const char *path,
 		else if (!prefixcmp(buf, "======="))
 			hunk = 2;
 		else if (!prefixcmp(buf, ">>>>>>> ")) {
+			int one_is_longer = (one->nr > two->nr);
+			int common_len = one_is_longer ? two->nr : one->nr;
+			int cmp = memcmp(one->ptr, two->ptr, common_len);
+
 			hunk_no++;
 			hunk = 0;
-			if (memcmp(one->ptr, two->ptr, one->nr < two->nr ?
-						one->nr : two->nr) > 0) {
+			if ((cmp > 0) || ((cmp == 0) && one_is_longer)) {
 				struct buffer *swap = one;
 				one = two;
 				two = swap;

t/t4200-rerere.sh

@@ -35,7 +35,8 @@ git commit -q -a -m first
 
 git checkout -b second master
 git show first:a1 |
-sed -e 's/To die, t/To die! T/' -e 's/life;$/life./' > a1
+sed -e 's/To die, t/To die! T/' > a1
+echo "* END *" >>a1
 git commit -q -a -m second
 
 # activate rerere
@@ -53,7 +54,7 @@ test_expect_success 'no postimage or thisimage yet' \
 test_expect_success 'preimage has right number of lines' '
 
 	cnt=$(sed -ne "/^<<<<<<</,/^>>>>>>>/p" $rr/preimage | wc -l) &&
-	test $cnt = 10
+	test $cnt = 9
 
 '
 
@@ -75,10 +76,10 @@ cat > expect << EOF
  For in that sleep of death what dreams may come
  When we have shuffled off this mortal coil,
  Must give us pause: there's the respect
+ That makes calamity of so long life;
 -<<<<<<<
--That makes calamity of so long life.
 -=======
- That makes calamity of so long life;
+-* END *
 ->>>>>>>
 EOF
 git rerere diff > out