Command line UI now handles EOF during request/response interactions.

For example
  $ echo | ./bin/hk.py -c 'new_playlist'
                       -c 'glob_curves_to_playlist test/data/*' --persist
used to loop forever thinking it was getting invalid responses to
  Exit? [y/N]

Also, change str() to unicode() in DoCommand.__call__ to handle
non-ascii messages (e.g. µ (micro) from SI units).