So. First pass. Add secondary explosions to RateExplosion and RateShotgun. Not yet added to shoves. This is of limited utility at present since the dX has to be small since we can't bother tracing all hog motion. But, should be more useful once shove is added, and tracking of explosives and mines.

foreach(dir "Fonts" "Forts" "Graphics" "Locale" "Maps" "Music" "Sounds" "Themes" "Missions" "Names" "misc" "Scripts")
  add_subdirectory(${dir})
endforeach(dir)