Working on the ether/USB problem.  The network can now be disabled (#define NETWORK in Configuration.h).  With it disabled the USB works with or without a network cable plugged in.  With it enabled the USB only works with a network cable plugged in too.  You have to wait for the ether to reinitialise (ether socket lights go out for a couple of secs, then come on, then the green one starts flashing) before trying to talk via the USB.  The ether is initialised before config.g is run, so the IP is the one defined in platform.h.  The network is disabled in this commit.  The heaters are set on by 0, not 1 (i.e. Duet board v0.6 or later).  To change this see #define HEAT_ON in platform.h