There were a couple remaining calls to getpass() still using Unicode

strings, and plenty of Unicode entries in environment variables. These

broke on Windows, since the implementation there expects byte strings.
This changes the last getpass() calls and normalizes all environment

variables on Windows prior to calling subprocess.Popen().

Installed a build on Windows. I triggered the authentication paths to

ensure getpass() was called in each case. I also triggered several

execute() paths, all of which worked without blowing up.