release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/os_msdos.txt b/runtime/doc/os_msdos.txt
index ea3842c..67821ed 100644
--- a/runtime/doc/os_msdos.txt
+++ b/runtime/doc/os_msdos.txt
@@ -1,4 +1,4 @@
-*os_msdos.txt*  For Vim version 8.2.  Last change: 2016 Feb 26
+*os_msdos.txt*  For Vim version 9.0.  Last change: 2016 Feb 26
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar