Chunky threads are now labeled by world (so for example you can identify and adjust their priority more easily via system tools such as htop). Also fixes 2 minor issues: 1) an overflow issue that could occur when entering an extremely large radius, causing a "negative ETA" to be shown, and 2) preventing the center or radius to be set to values above +/- 30 million, which is the hard limit in Minecraft where chunks will no longer generate.