fix WINDOWS-8 UTF-8 username encoding

>>> psutil.users()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Users\Démo\Desktop\psutil-2.1.3\psutil\__init__.py", line 1820,
in us
ers
return _psplatform.users()
File "C:\Users\Démo\Desktop\psutil-2.1.3\psutil\_pswindows.py", line
184, in u
sers
rawlist = cext.users()
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe9 in position 1:
invalid
continuation byte

>>> psutil.users()
[suser(name='Démo', terminal=None, host='0.249.23.1',
started=1419776716.0)]