Fix twoway_merge that passed d/f conflict marker to merged_entry().

When switching from one tree to another, we should not send a
marker that says "this file does not exist in the new tree -- I
am a placeholder to tell you that, and not a real blob" down to
merged_entry() as the result of the merge.

Author: Junio C Hamano

unpack-trees.c

@@ -711,20 +711,26 @@ int twoway_merge(struct cache_entry **src,
 		struct unpack_trees_options *o)
 {
 	struct cache_entry *current = src[0];
-	struct cache_entry *oldtree = src[1], *newtree = src[2];
+	struct cache_entry *oldtree = src[1];
+	struct cache_entry *newtree = src[2];
 
 	if (o->merge_size != 2)
 		return error("Cannot do a twoway merge of %d trees",
 			     o->merge_size);
 
+	if (oldtree == o->df_conflict_entry)
+		oldtree = NULL;
+	if (newtree == o->df_conflict_entry)
+		newtree = NULL;
+
 	if (current) {
 		if ((!oldtree && !newtree) || /* 4 and 5 */
 		    (!oldtree && newtree &&
 		     same(current, newtree)) || /* 6 and 7 */
 		    (oldtree && newtree &&
 		     same(oldtree, newtree)) || /* 14 and 15 */
 		    (oldtree && newtree &&
-		     !same(oldtree, newtree) && /* 18 and 19*/
+		     !same(oldtree, newtree) && /* 18 and 19 */
 		     same(current, newtree))) {
 			return keep_entry(current, o);
 		}