Added FixRad() function.

Function keeps radians in the range of (-PI, PI)
Physics problem: Added debug variables and messages.
Local variables declared as static.
Modified minimum spawn range for bonuses to 30 pixels.
Player motion now calculated in realtime.

There are still physics problems with direction vectors incorrectly
being resolved. With this commit player controlled vehicles no longer us
the precomputed sin/cos tables but a 'motion_angle' variable that holds
the movement direction angle.