Allow pages to be renamed fully. If the different title would cause

Allow pages to be renamed fully.  If the different title would cause
a change in URL, then we create a new page and make the old page into
a redirect to the new page.  However there is a problem that this
doesn't work properly if you rename a page then rename it back to the
original - the code would need to be smarter to work out what to do in
this situation.

404 page no longer uses the user-defined stylesheet (fixes a problem
on the Merjis site, for instance).