#8175 Better permission handling for non-existent wiki pages
End-users from time to time follow a link to a non-existing wiki page. Currently wikis try to create a new page, but you have to be logged in, so it prompts you to log in. But then even if you create an account & log in, you get a 403 Permission denied.
I think we should just show a 404 if a wiki page doesn't exist, and you don't currently have permission to create one.
db/8175
Looks good, merged.