By John S. McClenahen For the past few months Global Insight, a Waltham, Mass.-based economic forecasting firm, has been relatively optimistic about U.S. recovery from recession. Now it's even more so. Global Insight's economists expect GDP to grow at an annual rate of 4.2% during the second half of this year -- an annual rate of 3.8% in the third quarter and 4.5% in the fourth. In the meantime, however, Global Insight doesn't anticipate much in the way of job creation. Although the forecasting firm's economists expect to see payroll employment rise in the third quarter of this year, after several quarters of decline, the increase, they say, is likely to be at only a 0.4% annual rate.