Added new osg::TextureBase, osg::Texture1D, osg::Texture2D, and osg::Texture3D

classes, and changed osg::Texture and osg::TextureCubeMap so that they now derive
from osg::TextureBase.

src/osgUtil/CullVisitor.cpp

@@ -938,7 +938,7 @@ ImpostorSprite* CullVisitor::createImpostorSprite(Impostor& node)
         stateset->setRenderBinDetails(1,"DepthSortedBin");
     }
     
-    Texture* texture = impostorSprite->getTexture();
+    Texture2D* texture = impostorSprite->getTexture();
 
     // update frame number to show that impostor is in action.
     impostorSprite->setLastFrameUsed(getTraversalNumber());