merge-recursive: Save D/F conflict filenames instead of unlinking them

Rename make_room_for_directories_of_df_conflicts() to
record_df_conflict_files() to reflect the change in functionality.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/merge-recursive.h b/merge-recursive.h
index 7e1e972..58f3435 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -26,6 +26,7 @@
 	struct strbuf obuf;
 	struct string_list current_file_set;
 	struct string_list current_directory_set;
+	struct string_list df_conflict_file_set;
 };
 
 /* merge_trees() but with recursive ancestor consolidation */