some improvements

FuckAdBlock 2.1 fork - some modifications to the original script:
- removed automatic check at beginning because was failing in my case (window onload)
- added function "removeAll()" to detach all the callbacks (to be able to conveniently use anonymous functions passed by value)
- removed the "body" closure and using document.body everywhere instead (trying to initialize the closure var on window load was kinda not always working)