scanner: support help and --help
scanner: support help and --help

wayland-scanner without arguments prints out usage. With help or --help it
waits for stdin to supply something which isn't quite as informative as
printing out the help.

This patch also moves the strcmp for args up to have all of them in one
location.

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