Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index e6e225a..e263e6b 100644
--- a/runtime/doc/diff.txt
+++ b/runtime/doc/diff.txt
@@ -1,4 +1,4 @@
-*diff.txt*      For Vim version 8.0.  Last change: 2017 Oct 03
+*diff.txt*      For Vim version 8.1.  Last change: 2017 Oct 03
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar