i592: Use full path in various places

i592: Use full path in various places

When running mediagoblin in a sub path on a web server,
most things inside mediagoblin need the "inside path", but
when generating URLs for the webbrowser, full paths are
needed.

urlgen and routes already do that.

Some (mostly pagination and login) need the URL of the
current page. They used request.path_info. But this is the
"inside" path, not the full.

So now there is request.full_path and its used in various
places.