"Special" project issue views filters only work for exposed filters

The views filters for issue status and version support some "special" values: "- Open issues -" for the status, and the version series values for the version filter (e.g. "6.x issues"). Currently, these are mapped back to real values via accept_exposed_input(). That's silly, since it only works for exposed filters. ;) We should really do this magic mapping in query(), which, now that I code it, is vastly less complicated, anyway...