Error is now raised via req.error helper, which automatically adds already known info (method, request id), thus calls are terser.
Client's Error communicates request id, if received from server.
exc_info made explicit everywhere. Automatic exc_info gathering sometimes returned bogus info about unrelated exception from far before.

Fixed multiple HTTP args encoding/parsing, store_event now uses SQL placeholders, more robust fetching of cat/tag in store_event, simplified map_id usage