v0.18.3
Speed up importing of past.translation (issue #117)
Remove import of dummy_thread from _thread module (issue #124)
Prepare for 0.18.3 release
Future-proof for Py4.0
app engine compatibility: handle missing httplib._CS_* constants
Fix bug in fix_print.py fixer
Fix future import ordering
import from old imp library on older python versions
Fix for issue #262 (non-existing tkinter imports in older py27 versions)
Make the src folder a package (for the same of importing src.future.__version__ etc. from setup.py)