Misc fixes.

Closes a few old youtrack issues which I don't remember because I had
like 30 tabs open, and a few other issues which I found while testing
some of those.

worldedit-core/src/main/java/com/sk89q/worldedit/session/SessionManager.java

@@ -261,6 +261,7 @@ public class SessionManager {
      */
     public synchronized void unload() {
         clear();
+        timer.cancel();
     }
 
     /**