The Boston Business Journal recently noticed a trend of European entrepreneurs coming to the U.S. early in the lives of their companies, or establishing U.S. beachheads in Boston. Which has me wondering: How soon in the life of your startup should you be thinking about going global? Is it enough to concentrate on being a hit in your home market, or is that single-country focus really a risk? It’s a well documented fact that barriers to launching a new company …