No longer require sendmail.

No longer require sendmail.
Replace sendmail's `mail-text' by `rfc822-goto-eoh'.  (Bug#5174)
(report-emacs-bug-orig-text): Doc fix.
(report-emacs-bug-send-command, report-emacs-bug-send-hook):
New local variables, to adapt to different mail-user-agents.
(report-emacs-bug): Fix test for a gnu.org address.
Use overlays for emphasis, since font-lock defeats 'face property.
Pretest bugs also end up at the newsgroup these days.
Stop message-mode stripping text properties.
Set and use the new buffer-local variables.
(report-emacs-bug-hook): Add doc-string.
Remove some unnecessary save-excursions and simplify.
Use the appropriate hook and send-command.