[9fans] 9atom usb install improvements

[erik quanstrom]

i've fixed a few typos and bugs and knocked off a few sharp edges
in the 9atom usb install process which is more fully described here
        http://9fans.net/archive/2013/10/151

the build process still not always smooth due to /sys/src/cmd/runetype
occasionally failing to downloading the unicode data directly.

- erik