Restructured inheritance of BSD network classes

Now all BSD network classes directly inherit from Network as well as from the generic BSD network class.  This removes the need for itersubclasses().

library/setup

@@ -602,46 +602,6 @@ class FreeBSDHardware(Hardware):
                 if s:
                     self.facts['devices'][d.group(1)].append(s.group(1))
 
-def itersubclasses(cls, _seen=None):
-    """
-    itersubclasses(cls)
-
-    Generator over all subclasses of a given class, in depth first order.
-
-    >>> list(itersubclasses(int)) == [bool]
-    True
-    >>> class A(object): pass
-    >>> class B(A): pass
-    >>> class C(A): pass
-    >>> class D(B,C): pass
-    >>> class E(D): pass
-    >>> 
-    >>> for cls in itersubclasses(A):
-    ...     print(cls.__name__)
-    B
-    D
-    E
-    C
-    >>> # get ALL (new-style) classes currently defined
-    >>> [cls.__name__ for cls in itersubclasses(object)] #doctest: +ELLIPSIS
-    ['type', ...'tuple', ...]
-    """
-    
-    if not isinstance(cls, type):
-        raise TypeError('itersubclasses must be called with '
-                        'new-style classes, not %.100r' % cls)
-    if _seen is None: _seen = set()
-    try:
-        subs = cls.__subclasses__()
-    except TypeError: # fails only when cls is type
-        subs = cls.__subclasses__(cls)
-    for sub in subs:
-        if sub not in _seen:
-            _seen.add(sub)
-            yield sub
-            for sub in itersubclasses(sub, _seen):
-                yield sub
-
 class Network(Facts):
     """
     This is a generic Network subclass of Facts.  This should be further
@@ -663,7 +623,7 @@ class Network(Facts):
 
     def __new__(cls, *arguments, **keyword):
         subclass = cls
-        for sc in itersubclasses(Network):
+        for sc in Network.__subclasses__():
             if sc.platform == platform.system():
                 subclass = sc
         return super(cls, subclass).__new__(subclass, *arguments, **keyword)
@@ -969,14 +929,14 @@ class GenericBsdIfconfigNetwork(Network):
             for item in ifinfo[ip_type][0].keys():
                 defaults[item] = ifinfo[ip_type][0][item]
 
-class DarwinNetwork(GenericBsdIfconfigNetwork):
+class DarwinNetwork(GenericBsdIfconfigNetwork, Network):
     """
     This is the Mac OS X/Darwin Network Class.
     It uses the GenericBsdIfconfigNetwork unchanged
     """
     platform = 'Darwin'
 
-class FreeBSDNetwork(GenericBsdIfconfigNetwork):
+class FreeBSDNetwork(GenericBsdIfconfigNetwork, Network):
     """
     This is the FreeBSD Network Class.
     It uses the GenericBsdIfconfigNetwork unchanged