[python3] _DebugFileWriter._write(): Simpler PY3 handling.
[python3] _DebugFileWriter._write(): Simpler PY3 handling.

--HG--
extra : transplant_source : %18%17Q%C0N%C6M_H%AC%E7D%EDG%87j%AFc%BFW

userzimmermann/robotframework,userzimmermann/robotframework,userzimmermann/robotframework,userzimmermann/robotframework,userzimmermann/robotframework