configure.ac: Bump version to 1.3.91 for the alpha release
configure.ac: Bump version to 1.3.91 for the alpha release

eyolfson/wayland,eyolfson/wayland,eyolfson/wayland,abooij/wayland,tulcod/wayland,abooij/wayland,tulcod/wayland,bitfactor/wayland,sir-murray/wayland,bitfactor/wayland,sir-murray/wayland,bitfactor/wayland,sir-murray/wayland,mchalupa/wayland,tulcod/wayland,mchalupa/wayland,mchalupa/wayland,abooij/wayland