By DANIEL BELOUMOU OLOMO / AFP It began as a form of music chanted at wakes to comfort mourners — now it is part of Cameroon’s cultural mainstream, and a powerful form of expression for its frustrated youth. It began as a form of music chanted at wakes to comfort mourners — now it is part of Cameroon’s cultural mainstream, and a powerful form of expression for its frustrated youth. Mbole (pronounced “em-bo-lay”) developed around a quarter of a century ago in poor districts of Yaounde, the central African nation’s capital. It began as a sort of back-and-forth at funeral vigils between a chant…