mu4e: support message-user-organization

Automatically include Organziation: if set and update when changing the context.

Fixes: issue #2112.

NEWS.org

@@ -45,6 +45,11 @@
       your hook-functions (or elsewhere) you can check if anything changed using
       the new variable ~mu4e-index-update-status~.
 
+    - `message-user-organization` can now be used to set the `Organization:`
+      header. See its docstring for details.
+
+    - undo is now supported across message-saves
+
     - a lot of the internals have been changed:
 
       - =mu4e= is slowly moving from using the =~= to the more common =--= separator

mu4e/mu4e-compose.el

@@ -281,6 +281,7 @@ removing the In-Reply-To header."
           (define-key map (kbd "C-S-u")   'mu4e-update-mail-and-index)
           (define-key map (kbd "C-c C-u") 'mu4e-update-mail-and-index)
           (define-key map (kbd "C-c C-k") 'mu4e-message-kill-buffer)
+	  (define-key map (kbd "C-c ;")   'mu4e-compose-context-switch)
           (define-key map (kbd "M-q")     'mu4e-fill-paragraph)
           map)))
 
@@ -643,10 +644,14 @@ when the buffer is in `mu4e-compose-mode':
 		     "Draft must be saved before switching context. Save?"))
             (unless (and (not force)
 			 (eq old-context (mu4e-context-switch nil name)))
-              ;; Change From field to user-mail-address
+	      ;; Change From / Organization if needed.
+	      (message-replace-header "Organization"
+				      (or (message-make-organization) "")
+				      '("Subject")) ;; keep in same place
               (message-replace-header "From"
 				      (or (mu4e~draft-from-construct) ""))
-              ;; Move message to mu4e-draft-folder
+
+	      ;; Move message to mu4e-draft-folder
               (if has-file
                   (progn (save-buffer)
                          (let ((msg-id (message-fetch-field "Message-ID"))

mu4e/mu4e-draft.el

@@ -607,6 +607,8 @@ You can append flags."
 (defun mu4e~draft-common-construct ()
   "Construct the common headers for each message."
   (concat
+   (when-let ((organization (message-make-organization)))
+     (mu4e~draft-header "Organization" organization))
    (when mu4e-user-agent-string
      (mu4e~draft-header "User-agent" mu4e-user-agent-string))
    (mu4e~draft-header "Date" (message-make-date))))

mu4e/mu4e.texi

@@ -2458,6 +2458,7 @@ when starting; see the discussion in the previous section.
                             :to "aliced@@home.example.com")))
           :vars '( ( user-mail-address	    . "aliced@@home.example.com"  )
                    ( user-full-name	    . "Alice Derleth" )
+                   ( message-user-organization . "Homebase" )
                    ( mu4e-compose-signature .
                      (concat
                        "Alice Derleth\n"
@@ -2473,6 +2474,7 @@ when starting; see the discussion in the previous section.
                           (string-match-p "^/Arkham" (mu4e-message-field msg :maildir))))
           :vars '( ( user-mail-address	     . "aderleth@@miskatonic.example.com" )
                    ( user-full-name	     . "Alice Derleth" )
+                   ( message-user-organization . "Miskatonic University" )
                    ( mu4e-compose-signature  .
                      (concat
                        "Prof. Alice Derleth\n"