bug#20325: convert "fixes:debbugs:123" in log to (Bug#123) in ChangeLog

[Paul Eggert]

Dmitry Gutov wrote:
> I think debbugs:NNN is a bit better than Bug#NNN. It's more specific.

Currently, if you put ' (Bug#1234)' in a commit message, Emacs VC (via 
.dir-locals.el's setting of log-edit-rewrite-fixes) alters this to 'Fixes: 
debbugs:1234'.  Looking at recent commits, it appears that this is commonly done 
in practice, though I don't know what keystrokes trigger this.

How do you commit changes involving bug numbers?  What Emacs commands do you 
use?  (I use vc-dwim, but evidently I'm in the minority.)  Perhaps the "obvious" 
information about what keystrokes to use should be put into CONTRIBUTE, and 
CONTRIBUTE should recommend "Fixes: debbugs:1234' instead of its current 
recommendation 'Fixes: bug#1234'.