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.)

Also fleshed out the entry on struct.iter_unpack.

now more accurate.

initialized with a default value.

Also, provide a minor hint to the compiler on how to group the xors.

The test is failing on one of the stable FreeBSD buildbots.  It seems
unlikely that the gc module would not be available, so switching to
_imp may not fix the problem.

I was confused by the text saying that read_events "iterated", since it
actually returns an iterator (that's what a generator does) that the
caller must then iterate.  So I tidied up the language.  I'm not sure
what the sentence "Events provided in a previous call to read_events()
will not be yielded again." is trying to convey, so I didn't try to fix that.

Also fixed a couple more news items.

Also add missing tests to test_pydoc.

Also update news entry for SMTPException; when I changed it from
IOError to OSError I forgot to update the news item.

And more news entry clarifications.

Also clarify some NEWS entries.

take two parameters.