If the economy remains sluggish and retailers are jittery about the holidays, they can take comfort in forecasts that consumers will buy more gifts online this season. Jupiter Research sees good tidings for e-tailers as a group, projecting that online sales between Nov. 1 and Dec. 31, will reach $13.1 billion, up 17 percent from last year\u2019s Christmas season take.Jupiter isn\u2019t alone in the forecast biz, of course. An even rosier view comes from Forrester Research, where researchers expect U.S. online consumer spending to reach $72.1 billion by the time the books close on 2002. That\u2019s up 41 percent over 2001. For this holiday season specifically, Forrester is forecasting $9.5 billion, up from $8.3 billion in 2001.