Gresham Streigel, senior producer on Glenn Beck’s Fox News show, has left the channel and joined FNC rival, MSNBC. Streigel, who has also worked for Fox News for 13 years on shows such as Your World with Neil Cavuto and Fox & Friends, is now working for David Shuster. Beck’s team was, reportedly, trying to push the producer out. It’s probably more likely that it’s someone simply following a paycheck…