I'm not sure of the historical reasons why the database backend is
configure in the 'db/backend_name' file but (to me) it doesn't seem like
the most logical place for it to be configured, and can often (for me at
least) be another thing that I forget to configure when setting up or
migrating a tracker instance.

I have attached at patch that moves the configuration of the database
backend from the 'db/backend_name' file to the 'config.ini' file.

This will break backwards compatibility, so I would suggest waiting
until the 1.6 "branch" before committing it.

In the mean time I welcome comments or discussion about the merits (or
not) of keeping the 'db/backend_name' file around.