Increase default value for imenu-auto-rescan-maxout

* lisp/imenu.el (imenu-auto-rescan-maxout): Increase default value to
  600000.  (Bug#18426)
* doc/emacs/programs.texi (imenu-auto-rescan-maxout): Add
  documentation for imenu-auto-rescan-maxout.

Copyright-paperwork-exempt: yes

doc/emacs/programs.texi

@@ -308,6 +308,10 @@ Rescanning happens automatically if you set @code{imenu-auto-rescan} to
 a non-@code{nil} value.  There is no need to rescan because of small
 changes in the text.
 
+@vindex imenu-auto-rescan-maxout
+  @code{imenu-auto-rescan} will be disabled in buffers that are larger
+than @code{imenu-auto-rescan-maxout} in bytes.
+
 @vindex imenu-sort-function
   You can customize the way the menus are sorted by setting the
 variable @code{imenu-sort-function}.  By default, names are ordered as

etc/NEWS

@@ -50,6 +50,11 @@ often cause crashes.  Set it to nil if you really need those fonts.
 ---
 *** New toggle 'ibuffer-do-toggle-lock', bound to 'L'.
 
+** Imenu
+
+---
+*** The value for 'imenu-auto-rescan-maxout' has been increased to 600000.
+
 ** Gnus
 
 ---

lisp/imenu.el

@@ -96,11 +96,11 @@ This might not yet be honored by all index-building functions."
   :type 'boolean
   :group 'imenu)
 
-(defcustom imenu-auto-rescan-maxout 60000
-  "Imenu auto-rescan is disabled in buffers larger than this size (in bytes).
-This variable is buffer-local."
+(defcustom imenu-auto-rescan-maxout 600000
+  "Imenu auto-rescan is disabled in buffers larger than this size (in bytes)."
   :type 'integer
-  :group 'imenu)
+  :group 'imenu
+  :version "26.2")
 
 (defvar imenu-always-use-completion-buffer-p nil)
 (make-obsolete-variable 'imenu-always-use-completion-buffer-p