More JavaDoc improvements.

src/main/java/org/bukkit/event/player/PlayerCommandPreprocessEvent.java

@@ -2,6 +2,10 @@ package org.bukkit.event.player;
 
 import org.bukkit.entity.Player;
 
+/**
+ * Called early in the command handling process. This event is only
+ * for very exceptional cases and you should not normally use it.
+ */
 public class PlayerCommandPreprocessEvent extends PlayerChatEvent {
     public PlayerCommandPreprocessEvent(final Player player, final String message) {
         super(Type.PLAYER_COMMAND_PREPROCESS, player, message);