Update runtime files.
diff --git a/runtime/doc/message.txt b/runtime/doc/message.txt
index 5e47df1..1342265 100644
--- a/runtime/doc/message.txt
+++ b/runtime/doc/message.txt
@@ -1,4 +1,4 @@
-*message.txt* For Vim version 8.1. Last change: 2019 May 07
+*message.txt* For Vim version 8.1. Last change: 2019 May 18
VIM REFERENCE MANUAL by Bram Moolenaar
@@ -247,6 +247,9 @@
about the loss of information, set the 'fileencoding' option to another value
that can handle the characters in the buffer and write again. If you don't
care, you can abandon the buffer or reset the 'modified' option.
+If there is a backup file, when 'writebackup' or 'backup' is set, it will not
+be deleted, so you can move it back into place if you want to discard the
+changes.
*E302* >
Could not rename swap file