bug#9074: `report-emacs-bug' prompting rework

[Glenn Morris]

Version: 24.0.94

Lars Ingebrigtsen wrote:

> As previously discussed (like, a year ago), the prompting sequence when
> sending bug reports, especially from "emacs -Q", was kinda
> unsatisfactory.  (The main point was that it required that you had a
> valid-ish From header, even though you might end up sending the message
> through mailclient.el, which will then just rewrite your From header,
> anyway.)
>
> Fixing this required a bit of refactoring of the sendmail.el/Message
> setup functions, but hopefully I didn't screw up anything too badly.
>
> And the prompting sequence looks OK to me now, but please let me know if
> anything is wonky.