whatsnew: ssl getpeercert/do_handshake raise OSError, weakref __callback__.

whatsnew: ssl getpeercert/do_handshake raise OSError, weakref __callback__.

Also add a missing word to gc entry, and delete a now-obsolete doc note
in the weakref __callback__ docs.  (Opened an issue for rewriting
the section that compares finalizers and __del__ method.)