Democrat Martha Coakley, buoyed by her durable statewide popularity, enjoys a solid, 15-percentage-point lead over Republican rival Scott Brown as the race for US Senate enters the homestretch, according to a new Boston Globe poll of likely voters. Half of voters surveyed said they would pick Coakley, the attorney general, if the election were held today, compared with 35 percent who would pick Brown. Nine percent were undecided, and a third candidate in the race, independent Joseph L. Kennedy, received 5 percent. Coakley’s lead grows to 17 points - 53 percent to 36 percent - when undecideds leaning toward a...