adding energy limit

Hey All, first off awesome module. I'm building a "user feed" style view and am using radioactivity. My only issue was that a new node could potentially not be at the top of the feed if there were other nodes with lots of energy.

I solved this by adding a limit to the energy (say 1000) which everything starts off at. This way any new node will be at the top of the feed, and if tied I add another sort by last comment time.

With a fast decay the new node will drop off the top fast while other nodes with energy will stay at the top. I will need to dial in the other parameters, but this approach should work. May be worthwhile to add a limit to energy in future versions.

I made this change by modifying the update sql by adding a conditional limit in the radioactivity.inc:
SET energy= IF( energy+%f < 1000, energy+%f, 1000 )