Alan Spitalnik, a Jewish truck driver for the Parks Department on Staten Island, says he walked into a break room at Forestry Division headquarters last Wednesday to find three tree pruners performing an anti-Semitic skit for eight co-workers, who all "burst out laughing" when he entered. A source tells the Daily News that one worker wore a motorcycle helmet emblazoned with a swastika, another had a Hitler-style mustache, and the third comically brandished a flaming......