Freddie Mac finished off its comeback year in 2005 with a December buying spree, adding $17.26 billion to its retained portfolio that pushed the company’s holdings over the $700 billion mark for the first time ever – and within earshot of its rival Fannie Mae. While Freddie’s portfolio rebounded from a very sluggish 1.2 percent growth rate in 2004, debate continues to rage over proposals to scale back the massive holdings of the two government-sponsored…