improve error message for unsuitable polyline uploads

		if ( $min_dist{$key} ) {

			if ( defined $polyline->[ $min_dist{$key}{index} ][2] ) {

				return sprintf(

					'Error: Stop IDs %d and %d both map to lon %f, lat %f',

'Error: Route stops %d and %d both map to polyline lon/lat %f/%f. '

					  . 'The uploaded polyline must cover the following route stops: %s',

					$polyline->[ $min_dist{$key}{index} ][2],

					$stop->[1],

					$polyline->[ $min_dist{$key}{index} ][0],

					$polyline->[ $min_dist{$key}{index} ][1]

					$polyline->[ $min_dist{$key}{index} ][1],

					join(

						q{ · },

						map {

							sprintf(

								'%s (ID %s) @ %f/%f',

								$_->[0],      $_->[1] // 'unknown',

								$_->[2]{lon}, $_->[2]{lat}

							)

						} @{$route}

					),

				);

			}

			$polyline->[ $min_dist{$key}{index} ][2]