Fix copy marking from diffcore-rename.

When (A,B) ==> (B,C) rename-copy was detected, we incorrectly said
that C was created by copying B.  This is because we only check if the
path of rename/copy source still exists in the resulting tree to see
if the file is renamed out of existence.  In this case, the new B is
created by copying or renaming A, so the original B is lost and we
should say C is a rename of B not a copy of B.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -955,7 +955,9 @@ static void diff_resolve_rename_copy(void)
 			}
 			/* See if there is some other filepair that
 			 * copies from the same source as us.  If so
-			 * we are a copy.  Otherwise we are a rename.
+			 * we are a copy.  Otherwise we are either a
+			 * copy if the path stays, or a rename if it
+			 * does not, but we already handled "stays" case.
 			 */
 			for (j = i + 1; j < q->nr; j++) {
 				pp = q->queue[j];