1. Ensure that "rollback" respects locked pages.
2. Expire revisions of an edited page. Use a before_save
hook to deal with the situation where a page's name
has been changed.
Added the ability to rename existing pages.
[[!redirects Some Page Name]] redirects Wikilinks [[Some Page Name]] to
the current page (assuming "Some Page Name" does not exist).
Real pages trump redirects (though this may change, depending on
user feedback).
