[airstrike] Airstrike on glSDL

[Ulf Ekström]

Ok, here's the merged todo:

> > Game TODO:

> > Before release:
> > Menu system [Ulf]
> > Biplane AI [Ulf, anyone else?]
> > Game logic [Eero/Ulf/Everyone]
> > The damaged plane model is lost.. [Ulf]
> > Persistent configuration [Ulf]
> - More sprite generator types: [Eero]
>   - Possibility to specify in level file the player positions and
>     and how many lives player has on each level
>     - Checking when player has run out of lives
>   - Changing sprites & levels to use generators
> - Add fuel for each level (as I had modified biplanes so that they
>   have only limited amount of fuel) [Eero]
> - Handle level changes:
>   - Clearing objects, showing level end stats etc [Ulf?]
> - Add missing command line arguments (fullscreen etc)  [Ulf]

After release:

> > Weapons

> Triggers, possibility to transfer objects with other objects, transferring
> AIs (user control) from one sprite to another, particle effects, more
> levels & sprites etc. stuff 

Ulf