Added bombs back to biplane

[Eero Tamminen]

Hi,

I added the bombs back to biplane and key to AIs for dropping them (was 
surprisingly trivial, about all the code was already there :)).  At the
same time I finetuned the keyboard settings a bit to what I liked more.

Player 1:
- right shift: fire
- right ctrl: drop

Player 2:
- q: accelerate
- a: break
- x: left
- c: right
- left alt: fire
- tab: drop

Levels 1 & 2 have now a second player.

Ulf, how I set the second player plane to have different color and to head
into a different direction?


Next I'm going to look into getting a bomb as a bonus and disabling plane 
handling once it's gotten too much damage.

	 - Eero