* Optimized garbage collection of radiation sources until we get qdel() hints.
* Made the RADIATION_LOWER_LIMIT configurable (option for people to save some cpu time)
* Added some comments and broke the proccessor into separate procs for profiling purposes
* Added a changelog.
* The performance of the radiation controller as-is was not fast enough for inclusion in production servers, but it has some nice featuers, so rewrote it to be more performant.
* Instead of storing the radiation strength for every turf, we only store the sources of radiation, and calculate the strength only for mobs who might be in range.
* Old method was ray-tracing to every turf in range whether anything was there to be irradiated or not. Could be hundreds of turfs. New method only lazily calcualtes strength at a turf if we actually need to know it. Often times this is zero turfs if nobody is standing in engineering.
* Removed the automatic processing of objects with "rad_power" set. Objects are responsible for calling the repository to create/update their radiation sources. Saves some extra overhead that in practice was redundant with other process controllers.
* Also tweaked to be more respectful of qdel'd objects and added some comments.
