Aggressive three-way merge: fix D/F case

When the ancestor used to have a blob "P", your tree removed it, and the
tree you are merging with also removed it, the agressive three-way cleanly
merges to remove that blob.  If the other tree added a new blob "P/Q"
while removing "P", it should also merge cleanly to remove "P" and create
"P/Q" (since neither the ancestor nor your tree could have had it, so it
is a typical "created in one").

The "aggressive" rule is not new anymore.  Reword the stale comment.

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

t/t6035-merge-dir-to-symlink.sh

@@ -74,7 +74,7 @@ test_expect_success 'setup a merge where dir a/b-2 changed to symlink' '
 	git tag test2
 '
 
-test_expect_failure 'merge should not have conflicts (resolve)' '
+test_expect_success 'merge should not have conflicts (resolve)' '
 	git reset --hard &&
 	git checkout baseline^0 &&
 	git merge -s resolve test2 &&

unpack-trees.c

@@ -767,7 +767,8 @@ int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 		remote = NULL;
 	}
 
-	/* First, if there's a #16 situation, note that to prevent #13
+	/*
+	 * First, if there's a #16 situation, note that to prevent #13
 	 * and #14.
 	 */
 	if (!same(remote, head)) {
@@ -781,7 +782,8 @@ int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 		}
 	}
 
-	/* We start with cases where the index is allowed to match
+	/*
+	 * We start with cases where the index is allowed to match
 	 * something other than the head: #14(ALT) and #2ALT, where it
 	 * is permitted to match the result instead.
 	 */
@@ -811,12 +813,13 @@ int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 	if (!head && !remote && any_anc_missing)
 		return 0;
 
-	/* Under the new "aggressive" rule, we resolve mostly trivial
+	/*
+	 * Under the "aggressive" rule, we resolve mostly trivial
 	 * cases that we historically had git-merge-one-file resolve.
 	 */
 	if (o->aggressive) {
-		int head_deleted = !head && !df_conflict_head;
-		int remote_deleted = !remote && !df_conflict_remote;
+		int head_deleted = !head;
+		int remote_deleted = !remote;
 		struct cache_entry *ce = NULL;
 
 		if (index)