Fix login destination URL redirect

SpaceMan uses 'dest' for the target URL, while novabar was using 'target'.  This makes novabar use SpaceMan's 'dest' form variable.  This should fix redirection when logging in when viewing the wiki.  Currently it redirects you to the homepage (/, docroot, which redirects to /blog).

I'm guessing this was a think-o, I did a quick grep across the public website, I didn't see anything that actually used 'target'.