As the race to fill Ted Kennedy’s Senate seat unexpectedly tightens, political all-stars are flocking to Massachusetts to stump for the candidates. Bill Clinton took a break from relief efforts in Haiti to speak on behalf of Martha Coakley, the Democrat whose election looked to be a shoo-in just a few weeks ago. “You just have to decide whether you want us to be a tomorrow country or a yesterday country,’’ Clinton said, adding that helping Haiti and helping Coakley were “two sides of the same coin,” because they show the need for good governance. Meanwhile, Rudy Giuliani stumped for surging GOP candidate Scott Brown, and told a Boston crowd that “I’m used to being here with winning candidates,” referring to his appearances for governors Mitt Romney and William Weld. The campaign is high-stakes because Democrats can’t afford to lose a single vote on the health-care bill, and Brown has pledged to vote against it. President Obama will head to Massachusetts Sunday to campaign for Coakley.