configure.ac: re-bump version to 1.6.92 for rc1 release
configure.ac: re-bump version to 1.6.92 for rc1 release

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