Enable proxies (Self/Parent) for specifying ports.

Significant revamp of Port code.
Some cleanup of SimObject code too, particularly to
make the SimObject and MetaSimObject implementations of
__setattr__ more consistent.
Unproxy code split out of print_ini().

src/python/m5/multidict.py:
    Make get() return None by default, to match semantics
    of built-in dictionary objects.

--HG--
extra : convert_revision : db73b6cdd004a82a08b2402afd1e16544cb902a4

src/python/m5/multidict.py

@@ -29,7 +29,6 @@
 __all__ = [ 'multidict' ]
 
 class multidict(object):
-    __nodefault = object()
     def __init__(self, parent = {}, **kwargs):
         self.local = dict(**kwargs)
         self.parent = parent
@@ -102,14 +101,11 @@ class multidict(object):
     def values(self):
         return [ value for key,value in self.next() ]
 
-    def get(self, key, default=__nodefault):
+    def get(self, key, default=None):
         try:
             return self[key]
         except KeyError, e:
-            if default != self.__nodefault:
-                return default
-            else:
-                raise KeyError, e
+            return default
 
     def setdefault(self, key, default):
         try: