extensions mega_2560: allow "sudo" to work correctly

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
extensions mega_2560: add wifi wf111 support

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
build_sd.sh: fix usage message

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
build_sd.sh: add "done" message in the end
data: add OpenWRT binaries files (& other minor fixes in existing files)

Signed-off-by: Rodolfo Giometti <giometti@linux.it>