Emacs git-mode feature request: support fill-paragraph correctly

[Peter Simons <simons@cryp.to>]

Hi,

when I choose to commit in Emacs' git mode, I'm prompted to enter a
commit message in a buffer that looks something like this:

   Author: Joe Doe <joe.doe@example.org>
   --- log message follows this line ---
   foo.txt: lots of important changes

Now, when I hit M-q (fill-paragraph), Emacs doesn't recognize that
the "--- log message ..." line ought to be considered a paragraph
separator. As a result, the re-filled buffer is messed up:

   Author: Joe Doe <joe.doe@example.org> --- log message follows
   this line --- foo.txt: lots of important changes

Other modes, such as message-mode, do support that kind of thing
correctly, so apparently it is possible to configure what the editor
considers as a paragraph. Is there some Emacs wizard out there who'd
be kind enough to improve git-mode accordingly?

Take care,
Peter