Add an isValid() method to Entity. Addresses BUKKIT-810

src/main/java/org/bukkit/entity/Entity.java

@@ -129,6 +129,13 @@ public interface Entity extends Metadatable {
      */
     public boolean isDead();
 
+    /**
+     * Returns false if the entity has died or been despawned for some other
+     * reason.
+     * @return True if valid.
+     */
+    public boolean isValid();
+
     /**
      * Gets the {@link Server} that contains this Entity
      *

src/test/java/org/bukkit/plugin/messaging/TestPlayer.java

@@ -760,4 +760,8 @@ public class TestPlayer implements Player {
     public boolean hasLineOfSight(Entity other) {
         throw new UnsupportedOperationException("Not supported yet.");
     }
+
+    public boolean isValid() {
+        throw new UnsupportedOperationException("Not supported yet.");
+    }
 }