Mostly functional haptics/force feedback:
* Weapon firing kickback
* BFG warm-up 
* Hexen earthquakes
* Chainsaw idle (not happy with it yet, buzz is too random for it)

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2553 86ba831e-150c-0410-ab35-e06eaae15ed9