ETSource: Remove Jython 2.5 compatibility, fix Python 3 support.
ETSource: Remove Jython 2.5 compatibility, fix Python 3 support.

- No need to open and close files ourselves anymore.
- Use BytesIO instead of StringIO (except with IronPython) so support Python 3.

joongh/robotframework,joongh/robotframework,synsun/robotframework,snyderr/robotframework,snyderr/robotframework,jaloren/robotframework,HelioGuilherme66/robotframework,jaloren/robotframework,robotframework/robotframework,alexandrul-ci/robotframework,moto-timo/robotframework,alexandrul-ci/robotframework,moto-timo/robotframework,robotframework/robotframework,jaloren/robotframework,jaloren/robotframework,moto-timo/robotframework,synsun/robotframework,snyderr/robotframework,joongh/robotframework,alexandrul-ci/robotframework,alexandrul-ci/robotframework,joongh/robotframework,snyderr/robotframework,synsun/robotframework,synsun/robotframework,HelioGuilherme66/robotframework,moto-timo/robotframework,jaloren/robotframework,robotframework/robotframework,joongh/robotframework,alexandrul-ci/robotframework,synsun/robotframework,snyderr/robotframework,HelioGuilherme66/robotframework,moto-timo/robotframework