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).
For the file_list action, include the pages which link to the given file(s).
This required rejiggering so that that information is actually retained in the database.
Unfortunately, you'll actually need to revise the page(s) in question, because that's the
only time this information is updated in the database.
