patch 9.1.0864: message history is fixed to 200

Problem:  message history is fixed to 200
Solution: Add the 'msghistory' option, increase the default
          value to 500 (Shougo Matsushita)

closes: #16048

Co-authored-by: Milly <milly.ca@gmail.com>
Signed-off-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/message.txt b/runtime/doc/message.txt
index 6453b95..69d8bc7 100644
--- a/runtime/doc/message.txt
+++ b/runtime/doc/message.txt
@@ -1,4 +1,4 @@
-*message.txt*   For Vim version 9.1.  Last change: 2024 Mar 13
+*message.txt*   For Vim version 9.1.  Last change: 2024 Nov 14
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -29,7 +29,7 @@
 				Clear messages, keeping only the {count} most
 				recent ones.
 
-The number of remembered messages is fixed at 200.
+The number of remembered messages is determined by the 'msghistory' option.
 
 								*g<*
 The "g<" command can be used to see the last page of previous command output.