merge-tree: fix typo in "both changed identically"

Commit aacecc3 (merge-tree: don't print entries that match "local" -
2013-04-07) had a typo causing the "same in both" check to be incorrect
and check if both the base and "their" versions are removed instead of
checking that both the "our" and "their" versions are removed.  Fix
this.

Reported-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Test-written-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-tree.c

@@ -302,7 +302,7 @@ static void unresolved(const struct traverse_info *info, struct name_entry n[3])
 static int threeway_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *info)
 {
 	/* Same in both? */
-	if (same_entry(entry+1, entry+2) || both_empty(entry+0, entry+2)) {
+	if (same_entry(entry+1, entry+2) || both_empty(entry+1, entry+2)) {
 		/* Modified, added or removed identically */
 		resolve(info, NULL, entry+1);
 		return mask;

t/t4300-merge-tree.sh

@@ -205,6 +205,19 @@ EXPECTED
 	test_cmp expected actual
 '
 
+test_expect_success 'file remove A, B (same)' '
+	cat >expected <<\EXPECTED &&
+EXPECTED
+
+	git reset --hard initial &&
+	test_commit "rm-a-b-base" "ONE" "AAA" &&
+	git rm ONE &&
+	git commit -m "rm-a-b" &&
+	git tag "rm-a-b" &&
+	git merge-tree rm-a-b-base rm-a-b rm-a-b >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'file change A, remove B' '
 	cat >expected <<\EXPECTED &&
 removed in remote