fix projectile position as interceptor breaks off

also if it closes
don't init Screen as 32bpp if wrong mode for HQX
don't erase projectile based on interceptor pos.

Make sure a projectile actually covers the distance it's supposed to travel,
regardless of whether the interceptor that fired it has pulled away.
Merge pull request #303 from hmaon/projectile_speed

Hit with all four fusion balls!