getpass.getpass() prompt on windows expects char not unicode

Traceback:
> File "C:\Python27\Lib\site-packages\fabric\network.py", line 488, in prompt_for_password
> new_password = getpass.getpass(password_prompt, stream)
> File "C:\Python27\Lib\getpass.py", line 95, in win_getpass
> msvcrt.putch(c)
> TypeError: must be char, not unicode

I've just converted the prompt text to ASCII with `password_prompt.encode('ascii','ignore')`, but perhaps there's a nicer solution. Haven't tested on Linux.