• Always flush explicitly when writing to the subprocess. In Python 2,
  newline characters cause flushes, and in Python 3 they don't seem to.
• Always convert to JSON and add a newline to responses while still in
  Python 2 or 3's native string type.
• Always encode('utf-8'). In Python 2, this is a no-op (str is already
  utf-8 encoded bytes) and in Python 3, this creates utf-8 encoded
  bytes from a unicode object.

Fixes evaluate().explore() hanging on Python 3 due to
newline characters not flushing the I/O buffer, and subsequent crashes
due to improperly encoded string objects after fixing the hang.