Feature summary (what you would like to be able to do and where):
Site.watched_pages() yields both content and talk pages which is senseless for a watchlist. For backward compatibility it should have a keyword parameter (defaulting to False) that lets the user get only the content pages.

Use case(s)):
Whatever one might do with a watchlist.

Benefits (why should this be implemented?):
A clearer list and less risk of error by processing the same item twice.

NB InvalidTitleError must be handled, see also T330786.