Whitney Tilson in an email to ValueWalk discusses his short 3D Systems Corporation (NYSE:DDD) postion, long magicJack VocalTec Ltd (NASDAQ: CALL) stake, and his annual returns. Whitney Tilson The Kase Fund finished 2013 with a gain of 16.6% and is off to a strong start this year, up slightly on the year vs. -2.5% for the S&P 500 (through today’s close). Attached is my 2013 annual letter, in which I discuss lessons learned and adjustments made (especially on the short side), how I’m casting a wider net, and my 10 largest long positions. 2) Attached is a brand-new, in-depth report I…