Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/os_dos.txt b/runtime/doc/os_dos.txt
index 1167e2a..b950953 100644
--- a/runtime/doc/os_dos.txt
+++ b/runtime/doc/os_dos.txt
@@ -1,4 +1,4 @@
-*os_dos.txt*    For Vim version 8.0.  Last change: 2006 Mar 30
+*os_dos.txt*    For Vim version 8.1.  Last change: 2006 Mar 30
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar