Added set/getUnrefImageOnApply() methods and associated flag and

code in Texture::apply() to set the _image to 0 on apply.  Note,
this will only work when you have a single graphics context, as
with multiple graphics contexts one can't delete the image after
the first apply, as there will be more than one texture object to
update.

src/osg/Texture.cpp

@@ -20,6 +20,7 @@ Texture::DeletedTextureObjectCache Texture::s_deletedTextureObjectCache;
 
 Texture::Texture():
     _target(GL_TEXTURE_2D),
+    _unrefImageAfterApply(true),
     _wrap_s(CLAMP),
     _wrap_t(CLAMP),
     _wrap_r(CLAMP),
@@ -223,6 +224,9 @@ void Texture::apply(State& state) const
         // unless a second bind is called?!!
         // perhaps it is the first glBind which is not required...
         glBindTexture( _target, handle );
+        
+        if (_unrefImageAfterApply)
+            _image = 0;
 
     }
 }