* (bug 4201) Fix user-talk mode for Enotif, and general code cleanup

* (bug 4201) Fix user-talk mode for Enotif, and general code cleanup
- treat NULL properly in watchlist lookup for notification sending
- consolidate a lot of ugly code that fiddles in those tables
- use user_newtalk consistently in enotif mode; watchlist for email notifications, user_newtalk for on-screen message and status check
- clean up handling of other peoples' user_talk pages when in the talk-only limited enotif: only your own will get sent, not other people watching your page
- and others watching your page _will_ work in watchable enotif mode
- add a watch on page + talk page consistently for the auto-add of the user talk page, not just half the page
- don't unwatch the user talk page on view! that's just wacky
- removed UserTalkUpdate, now redundant
- have User::setNewTalk() apply immediately
- clear newtalk from User::clearNotification() and User::clearAllNotifications()