Add close_files() that closes all files

Renames the current implementation to close_and_free_files(), since
that is what it actually does.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index d7875b0..4fbc704 100644
--- a/fio.h
+++ b/fio.h
@@ -800,6 +800,7 @@
  * File setup/shutdown
  */
 extern void close_files(struct thread_data *);
+extern void close_and_free_files(struct thread_data *);
 extern int __must_check setup_files(struct thread_data *);
 extern int __must_check open_files(struct thread_data *);
 extern int __must_check file_invalidate_cache(struct thread_data *, struct fio_file *);