- Check for type compatibility before setting cell renderer attributes
	  - Clear cell renderer attributes before setting liststore column types and resync them after
	    (Avoids cricital warnings where the underlying data types changed and dont match the properties
	    of the renderers)
	  - Fill in the gaps in model data while loading some columns with non serializable types
	    (fixes severe bug: model data was loaded with missing columns of data).

	* plugins/gtk+/glade-column-types.c, plugins/gtk+/glade-model-data.c:
	  allow model data with explicitly G_TYPE_INVALID types.