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).
Deleting a page removes all revisions of that page.
Deleting a Web removes all pages (and all revisions thereof)
and all wiki_files belonging to that Web.
