Protected Trade/Quest system + Expirable quests

Added true protection against race conditions on player trades and fixed
some situational issues. Character's quest status table also received
concurrency treatment. Quests with time limit now expires properly.
Increased subtly the performance on the server start-up.

src/client/MapleClient.java

@@ -786,7 +786,7 @@ public class MapleClient {
 			final MapleGuild guild = player.getGuild();
 
 			if (channel == -1 || shutdown) {
-                                chrg.setCharacter(null);
+                                if(chrg != null) chrg.setCharacter(null);
                             
                                 removePlayer();
                                 player.saveCooldowns();