Compose window options

[Peter Bloomfield <PeterBloomfield bellsouth net>]

Laurent Duperval recently pointed out 
(http://bugzilla.gnome.org/show_bug.cgi?id=104144) an issue with the 
Options menu on the compose window: `Request Disposition Notification' 
is persistent, not per-message.  Laurent (correctly, imho) added `It 
should either affect only the current message, or be moved to the 
Preferences menu.'

The `Always Queue Sent Mail' is similarly persistent; the issue here is 
slightly different, as the prefs page already offers control over this 
option. However, the state of the toggle item on the menu isn't 
initialized with the global pref, and isn't updated if the pref is 
changed while a compose window is open: the toggle item merely replaces 
the current setting.

I've just added a `Format = Flowed' item to that menu, with what I 
believe to be the correct behavior: it's initialized with the state of 
the global pref when the compose window is opened, and can be used to 
override the global pref for the current message, but doesn't change 
the global pref itself and isn't updated if the global pref is changed 
while the compose window is open (OK, the last point was to avoid the 
complication of catching changes in the absence of notification!).

I propose that we change the other items to behave in this way.  
Comments?