bpo-17393: do not convert import of non-package by romuald · Pull Request #16826

bpo-17393: do not convert import of non-package by romuald · Pull Request #16826 · python/cpython

In lib2to3, when a patched code is importing a module that has the same
name as a local directory, check that it contains an __init__.py file
before converting it to a local import

Quick example:

```
fixtures/__init__.py
fixtures/json/things.json
```

Previously `import json` was converted to `from . import json`