mu4e: autoload major entry points

Autoload functions `mu4e' and `mu4e~compose-mail' and the definition of
the mail-user-agent `mu4e-user-agent'.  The last to are required so
that `compose-mail' can be used without explicitly loading mu4e.

Also require `mu4e' in mu4e-compose.el (after providing mu4e-compose
to avoid a circular dependencies).  This is required because the
autoload definitions only cause mu4e-compose but not mu4e to be loaded
when using `compose-mail', but if mu4e isn't loaded various handlers
are not loaded (and possibly there are other problems if mu4e is not
fully loaded).

mu4e/mu4e-compose.el

@@ -482,6 +482,7 @@ Ie. either 'name <email>' or 'email')."
 ;; mu4e-compose-func and mu4e-send-func are wrappers so we can set ourselves
 ;; as default emacs mailer (define-mail-user-agent etc.)
 
+;;;###autoload
 (defun mu4e~compose-mail (&optional to subject other-headers continue
 			   switch-function yank-action send-actions return-action)
   "This is mu4e's implementation of `compose-mail'."
@@ -515,6 +516,7 @@ Ie. either 'name <email>' or 'email')."
       (message-goto-body))))
 
 ;; happily, we can re-use most things from message mode
+;;;###autoload
 (define-mail-user-agent 'mu4e-user-agent
   'mu4e~compose-mail
   'message-send-and-exit
@@ -547,3 +549,7 @@ Ie. either 'name <email>' or 'email')."
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 (provide 'mu4e-compose)
+
+;; Load mu4e completely even when this file was loaded through
+;; autoload.
+(require 'mu4e)

mu4e/mu4e.el

@@ -71,6 +71,7 @@
 
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;;###autoload
 (defun mu4e ()
   "Start mu4e."
   (interactive)