1. Removed the unicode wrapper around fake_env io
2. Overrided pyfakefs cStringIO with StringIO (Python 2.x)
3. copy_dir will copy file in binary file to the fake filesystem
*unless* they are bib, yaml, txt or md files
4. ui.handle_exception() conserve traceback
Numerous unicode subtelties required diving into pyfakefs and configobj
source code. Unicode on Python 2.x is the worst.