Get rid of dict.has_key(). Boy this has a lot of repercussions!

Not all code has been fixed yet; this is just a checkpoint...
The C API still has PyDict_HasKey() and _HasKeyString(); not sure
if I want to change those just yet.

Lib/rfc822.py

@@ -428,10 +428,6 @@ def setdefault(self, name, default=""):
             self.dict[lowername] = default
             return default
 
-    def has_key(self, name):
-        """Determine whether a message contains the named header."""
-        return name.lower() in self.dict
-
     def __contains__(self, name):
         """Determine whether a message contains the named header."""
         return name.lower() in self.dict