syncs manual page and code (usage() incomplete)

also use EARGF(usage()) instead of just ARGF()

use /dev/*-files instead of kernel files directly (or are hard-coded kernel devices a good idea?)

/sys/src/cmd/usb/misc/usbprint can be removed (there is a /386/bin/usb/usbprinter on sources), usbprint in usb/misc is not installed.

to usbstart could be added: usb/usbprinter (as the manual page suggests).

mjl, [email protected]