what if tracker url changes?

[Stefan Monnier]

> * Define the emacs tracker builtin to bzr
> * Make it easier to define new tracker shortcuts in the versioned tree

Point nb 2 makes point nb 1 completely useless, so I'd rather skip point
nb 1 and go straight to point nb 2.
The one thing that is worth adding as a default bugtracker is a generic
bugtracker_uri_url = {id}
so people can use --fixes without any configuration (point nb2 will
make it less important as well, but not quite completely useless).
I'd encourage you to add it right away, including to maintenance
branches of Bzr.


        Stefan