Pyflakes

- Process function scope variable annotations for used names
- Find Python files without extensions by their shebang

- Enable support for PEP 526 annotated assignments

- Change formatting of ImportStarMessage to be consistent with other errors
- Support PEP 498 "f-strings"

- Fix PyPy2 Windows IntegrationTests
- Check for duplicate dictionary keys
- Fix TestMain tests on Windows
- Fix "continue" and "break" checks ignoring py3.5's "async for" loop

- Fix TypeError when processing relative imports

- Avoid traceback when exception is del-ed in except