Extract 'clean_files' function to 'helpers' module
Refactor auto-generated VF files cleaning
Add missed import
Py3: force using absolute imports and 'print' function

--HG--
extra : amend_source : 4f25f67be5fc6bb0317774d7536da2378c3faf14
Make SciPy building verbose on Travis CI
Merge changes from 'develop' branch