“Mama say ‘Yeah’” goes the hypnotic refrain of “Mama Say,” the third and final preview of inimitable UK-formed electro-Afro-funk group Ibibio Sound Machine’s hotly anticipated new record Pull the Rope (out May 3 on Merge). The song pulses with electronic drums and a grinding synth-bass line, with flourishes of retro keys that bring to mind late-70’s Nigeria-based Casio-pop lord William …