Bugfix [#33387] Smoke: Animating Smoke Type from Flow to None crashes blender

This property was never intended to be animatable. 
Workaround: Animate density.

TODO for 2.66: Introduce on/off property for flow and collision objects

source/blender/makesrna/intern/rna_modifier.c

@@ -2207,6 +2207,7 @@ static void rna_def_modifier_smoke(BlenderRNA *brna)
 	RNA_def_property_enum_sdna(prop, NULL, "type");
 	RNA_def_property_enum_items(prop, prop_smoke_type_items);
 	RNA_def_property_ui_text(prop, "Type", "");
+	RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
 	RNA_def_property_update(prop, 0, "rna_Smoke_set_type");
 }