Rewording the getheader method of HTTPResponse.

Doc/library/http.client.rst

@@ -465,9 +465,10 @@ statement.
 
 .. method:: HTTPResponse.getheader(name, default=None)
 
-   Get the contents of the header *name*, or *default* if there is no matching
-   header. If *default* is an iterator other than a string, then the return
-   value will be a string consisting of items of the iterator joined by comma.
+   Return the value of the header *name*, or *default* if there is no header
+   matching *name*.  If there is more than one  header with the name *name*,
+   return all of the values joined by ', '.  If 'default' is any iterable other
+   than a single string, its elements are similarly returned joined by commas.
 
 
 .. method:: HTTPResponse.getheaders()