Explicitly log exception from asynchronous tasks.

Previously an UnhandledException would be thrown and the stack trace / message would be printed to System.err in the default UncaughtExceptionHandler for ThreadGroup. This was undesirable as it meant that logging frameworks / exception monitors such as Sentry were unable to get the exception. Additionally it would cause the death of the thread in the ExecutorService. This change mimics the behaviour of exceptions occuring during synchronous tasks.

src/main/java/org/bukkit/craftbukkit/scheduler/CraftAsyncTask.java

@@ -3,12 +3,11 @@ package org.bukkit.craftbukkit.scheduler;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.Map;
+import java.util.logging.Level;
 
-import org.apache.commons.lang.UnhandledException;
 import org.bukkit.plugin.Plugin;
 import org.bukkit.scheduler.BukkitWorker;
 
-
 class CraftAsyncTask extends CraftTask {
 
     private final LinkedList<BukkitWorker> workers = new LinkedList<BukkitWorker>();
@@ -53,7 +52,8 @@ class CraftAsyncTask extends CraftTask {
             super.run();
         } catch (final Throwable t) {
             thrown = t;
-            throw new UnhandledException(
+            getOwner().getLogger().log(
+                    Level.WARNING,
                     String.format(
                         "Plugin %s generated an exception while executing task %s",
                         getOwner().getDescription().getFullName(),