Fixed issue with /allAtOnce being too aggressive on lighting, causing memory issues on low-memory servers.
allAtOnce mode now returns into the server briefly between ticks, allowing other commands (such as /cancelgen) to be run.
Using /fast or /veryfast modes on servers with low ram can cause runaway memory usage, exceeding 1gig. This is due to a bug in minecraft/craftbukkit. I've proposed a fix here: https://github.com/Bukkit/CraftBukkit/pull/501 -- In the meantime, using lower generation speeds is recommended for low ram servers or massive generations.
