[airstrike] Penguin animation for Airstrike

[Ulf Ekström]

Hi, I'm just back from a vacation, but will put out the new version of
Airstrike in a few days.

> I just made a penguin for Airstrike which walks.  

I was just waiting for this! Now we'll have to call the game TuxStrike :)
It looks very cute.

> Or maybe there could be an icefloat level where are igloos instead
> of huts and penguins instead of humans (receiving the mails).  On
> these levels cannons would naturally shoot snowballs :-).

I like this idea. It's probably even easier to model than the tropical
island theme. Maybe we can have an intro screen which is a earth-globe,
with the different levels marked on the globe? 

A small change I am considering is to have the number of frames
encoded in the filename of each animation, something like

pingu.16.png

Then it would be much easier to change the animations without
recompiling etc. But then we must use glob() to find the files. Do you
know a portable way to glob?

Regards,
Ulf