Vim 8.1 release

Update version number and information.  Fix a couple of tests.
diff --git a/runtime/doc/tabpage.txt b/runtime/doc/tabpage.txt
index 56d58eb..20dd1ef 100644
--- a/runtime/doc/tabpage.txt
+++ b/runtime/doc/tabpage.txt
@@ -1,4 +1,4 @@
-*tabpage.txt*   For Vim version 8.0.  Last change: 2018 Mar 29
+*tabpage.txt*   For Vim version 8.1.  Last change: 2018 Mar 29
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar