Various performance tweaks: cull nodes with no mesh children, allow

locking the transforms and bounds of models whose positions will not 
change, skip/postpone updates for models that aren't in view.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4078 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/jme/model/ModelSpatial.java

@@ -27,8 +27,6 @@ import java.io.IOException;
 import java.nio.MappedByteBuffer;
 import java.nio.channels.FileChannel;
 
-import java.util.HashMap;
-
 import com.jme.math.Matrix4f;
 import com.jme.renderer.Renderer;
 import com.jme.scene.Spatial;