Added an asPlayer method to LocalCommandSender, which casts the object to LocalPlayer if possible and throws an exception otherwise.

src/main/java/com/sk89q/worldedit/LocalPlayer.java

@@ -549,4 +549,8 @@ public abstract class LocalPlayer extends LocalCommandSender {
     public void dispatchCUIHandshake() {
     }
 
+    @Override
+    public LocalPlayer asPlayer() {
+        return this;
+    }
 }