bug#32680: 27.0.50; Improve docstring and customization for 'message-signature'

[Robert Pluim <rpluim@gmail.com>]

Philipp Stephani <p.stephani2@gmail.com> writes:

> The manual states
>
>    If you change ‘message-signature’ to ‘nil’, Emacs will not insert
> your mail signature automatically.  You can insert your mail signature
> by typing ‘C-c C-w’ (‘message-insert-signature’) in the mail buffer.
> Emacs will look for your signature in the signature file.
>
> However, the docstring for message-signature doesn't state that nil is a
> possible value, and the customization choices also don't suggest nil.

We could even put this in emacs-26.

2018-09-10  Robert Pluim  <rpluim@gmail.com>

	* lisp/gnus/message.el (message-signature): Allow nil as a
	customizable value, and describe its effect. (Bug #32680)

diff --git i/lisp/gnus/message.el w/lisp/gnus/message.el
index 66356b6fda..ec2286b06d 100644
--- i/lisp/gnus/message.el
+++ w/lisp/gnus/message.el
@@ -1079,12 +1079,15 @@ message-indent-citation-function
 (defcustom message-signature mail-signature
   "String to be inserted at the end of the message buffer.
 If t, the `message-signature-file' file will be inserted instead.
+If nil, no signature is inserted.
 If a function, the result from the function will be used instead.
-If a form, the result from the form will be used instead."
-  :version "23.2"
+If a form, the result from the form will be used instead.
+See `mail-signature' for the recommended format of a signature."
+  :version "27.1"
   :type '(choice string (const :tag "Contents of signature file" t)
 		 function
-		 sexp)
+		 sexp
+                 (const :tag "None" nil))
   :risky t
   :link '(custom-manual "(message)Insertion Variables")
   :group 'message-insertion)