Ronald Lockett, whose emotionally raw and politically trenchant paintings and assemblages are featured in “Fever Within: The Art of Ronald Lockett” at the American Folk Art Museum, did not have a lot going for him. Poor, young, black and with only a high school degree, he lived his whole life (1965-1998) in a working class suburb in Bessemer, Ala., and he died at 32 from AIDS-related pneumonia. But he had some things in his favor: talent, drive and a powerful role model residing two doors down the street in the form of an older cousin, Thornton Dial (1928-2016), one of the late 20th century’s most celebrated self-taught artists.