[reactive] Bounce

[Greg Fitzgerald]

I fixed the collision issue (I should have failed first year physics).

gravity :: Double -> Double -> TimeT -> (Double, Double)
gravity x0 v0 t = (x0 + v0 * t - 4.9 * (t * t), v0 - 9.8 * t)

New code here:
http://hpaste.org/12263

But this is still unusable.  There's a massive space leak somewhere,
and the program continues to grow even after you close the window!
Anyone have any pointers for tracking this down?

-Greg