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/wsgiref/headers.py

@@ -80,12 +80,10 @@ class Headers:
 
 
 
-    def has_key(self, name):
+    def __contains__(self, name):
         """Return true if the message contains the header."""
         return self.get(name) is not None
 
-    __contains__ = has_key
-
 
     def get_all(self, name):
         """Return a list of all the values for the named field.