Gee, wouldn't it be nice if [this](http://download.java.net/jdk8/docs/api/java/util/function/Consumer.html) was already in the default libraries? Oh well, go with what we got.

I already asked @ShadowDog007 to remove another second method, `isCancelled()`, on the grounds that it is easily replicated by a simple `if (condition) return;` at the beginning of accept(): https://github.com/Bukkit/Bukkit/pull/872#discussion_r5047367

Also, exactly *what do you expect to go wrong* in loading a chunk (or generating it, on the main thread, if it does not exist)? If we get an `IOException` during a chunk load, there's some bigger problem going on that a plugin really shouldn't be worrying about.