- Scene: give explicit return value to TextureSet callback. This worked just by accident.
- fix critical error that caused gl.Texture2D calls to be accidentally compiled into a displist, causing a massive performance hit until the displist was recompiled. The reworked flow no longer uploads textures implicitly. Instead, a call to Texture.Upload() is required and done before displists are compiled.
- Texture: improved Upload() code no longer creates a temporary Bitmap if the source Image is already a Bitmap instance.
- Texture: forgot to dispose the _image field.