After last year's revelry along the East River, Rooftop Films' annual Fourth of July blowout goes west — to the Chelsea Museum. Indeed, the museum's rooftop provides a felicitous setting to say cheers to the US of A, not only for its wondrous view of the city fireworks, but for its proximity to the piers that once inducted the foreign-born into democracy.  Preceding the tricolor pyrotechnics is a lively bill headlined by New Zealand's Bachelorette (aka Annabel Alpers), whose multilayered electro pop explores personal communication in the age of computerized reproduction. Closing out the night is a program of rousing shorts, with equal opportunity for comedy and politics.