regression: --demo

[Alexandre Detiste]

> I don't understand what happens here.
>
> Does this mean, it will not produce "wolf3d-full-v14-data" because it
> already produces "wolf3d-full-v12-data", although all the necessary data
> files for "wolf3d-full-v14-data" are available?

Yes, for now; it's better that build both and let "dpkg -i" explode.

> I beg to differ with your opinion WRT to "v1.4 data is not any better
> than v1.2". I think, if both data is available, the higher version
> should always get precedence.

Getting v1.2 to work alongside v1.4 needed quite extensive changes;
but the "prefered version" logic is not yet implemented.

I was thinking, how should we define this preference order:
- text comparaison of package name (bad)
- order of package as seen in yaml files (won't work if
self.yaml['packages'].items() is a dict)
- explicit "score" int (ugly)
- 'better_version:' pointer to an other package in same yaml, that
acts like 'demo_for:' ;
so I guess I'll go for this.