V1.11
  1) Bugfix: don't send garbage after SPI commands to FPGA.
     This fixes "LED shows random colors" problem and possibly some others;
  2) Bugfix: don't crash BFGMiner because of SPI communication errors.
     This possibly fixes frequent BFGMiner restarts;
  3) Improvement: Init last_nonce on die config.
     This possibly fixes "High number of rejects after die reconfig".