Bitcoin is about to get a big dose of legitimacy, something that could be helping to boost its price. Two of the world’s biggest exchanges will begin trading bitcoin futures, pushing it further into the mainstream. The digital currency started out the year below $1,000 but has rallied since then. Banks and financial companies have taken a keen interest in the concept, seeing uses for it in securities settlement, payments and other transactions far beyond tracking a digital token. But bitcoin has some obvious problems, extreme price volatility being just one.”]