WSGI application response body must be of type 'bytes'

[mmulich]

According to PEP3333 (the Python 3 version of PEP333), the body of a WSGI application must be in bytes (e.g. b""). Therefore, the fake socket implementation (wsgi_fake_socket) as well as the environment maker (make_environ) must be changed to handle bytes rather than strings (str).