python3: scrapy.__version__, NoneType, urlparse_monkeypatches

Python 3 compatibility changes:
1. `__version__` will be `str` in both 2 and 3. Necessary because pkgutil.get_data returns `bytes` in 3.
2. `NoneType` is not available in 3
3. Apply `urlparse_monkeypatches` in Python 2 only. Patches are not needed in 3 (tested in 3.2-3.4).