Fixed DrawCallback in Drawable and added CullCallback to Drawable

Cull Visitor now checks for a Drawable's CullCallback and calls it
if it exists.  It then prunes based on the return value (bool) of the
cull callback.

src/osg/Drawable.cpp

@@ -38,7 +38,8 @@ Drawable::Drawable(const Drawable& drawable,const CopyOp& copyop):
     _globjList(drawable._globjList),
     _bbox(drawable._bbox),
     _bbox_computed(drawable._bbox_computed),
-    _drawCallback(drawable._drawCallback)
+    _drawCallback(drawable._drawCallback),
+    _cullCallback(drawable._cullCallback)
 {}
 
 Drawable::~Drawable()

src/osg/Texture.cpp

@@ -191,6 +191,7 @@ void Texture::apply(State& state) const
         if (_subloadMode == OFF)
         {
             glBindTexture( GL_TEXTURE_2D, handle );
+            glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, _min_filter);
         }
         else  if (_image.valid() && _image->data())
         {

src/osgUtil/CullVisitor.cpp

@@ -895,11 +895,18 @@ void CullVisitor::apply(Geode& node)
     Matrix* matrix = getCurrentMatrix();
     for(int i=0;i<node.getNumDrawables();++i)
     {
-
         Drawable* drawable = node.getDrawable(i);
         const BoundingBox &bb =drawable->getBound();
 
-        if (isCulled(bb,mode)) continue;
+	if( drawable->getCullCallback() )
+	{
+	    if( drawable->getCullCallback()->cull( this, drawable ) == true )
+		continue;
+	}
+	else
+	{
+            if (isCulled(bb,mode)) continue;
+	}
 
 
         //SandB change: