python3 fixes for find_module, long, unicode

1. Wrap imp.find_module in a wrapper to automatically decode byte strings
2. long = int (long does not exist in python3)
3. Vim compatibility: Automatically decode byte strings as unicode in python3 scripts. We still use byte arrays by default, but plugin scripts expect Unicode
This needs to be `from ..compat import find_module, IS_PYTHON3` to pass on scrutinizer