[Urwid] Installing 0.9.8.3 with Python 2.6 fails

[Joern Koerner]

Hi again!

I tried to setup the current urwid within Python 2.6, which fails with the 
following error:

$python setup.py install
Traceback (most recent call last):
  File "setup.py", line 29, in <module>
    import urwid
  File "/root/urwid/urwid/__init__.py", line 49, in <module>
    from listbox import *
  File "/root/urwid/urwid/listbox.py", line 85, in <module>
    class SimpleListWalker(MonitoredList, ListWalker):
  File "/usr/lib/python2.6/abc.py", line 76, in __new__
    cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace)
TypeError: Error when calling the metaclass bases
    metaclass conflict: the metaclass of a derived class must be a (non-
strict) subclass of the metaclasses of all its bases