patch 9.1.0537: signed number detection for CTRL-X/A can be improved

Problem:  signed number detection for CTRL-X/A can be improved
          (Chris Patuzzo)
Solution: Add the new "blank" value for the 'nrformat' setting. This
          will make Vim assume a signed number only if there is a blank
          in front of the sign.
          (distobs)

fixes: #15033
closes: #15110

Signed-off-by: distobs <cuppotatocake@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index b60f386..d70c3b1 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Jun 20
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Jul 06
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41574,6 +41574,8 @@
 - the default for 'commentstring' contains whitespace padding to have
   automatic comments look nicer |comment-install|
 - 'completeopt' is now a |global-local| option.
+- 'nrformat' accepts the new "blank" suboption, to determine a signed or
+  unsigned number based on whitespace in front of a minus sign.
 
 							*added-9.2*
 Added ~