fix for 2 segfaults running in background mode.

- operators which reload G.main would crash blender if called from python and then accessed bpy.data.*
- WM_read_homefile_exec was setting the contexts Scene to NULL as a signal for the event system, this didnt work in background mode, crashing when property update functions expected scene to be set.

source/blender/python/intern/bpy_rna.h

@@ -110,4 +110,6 @@ int pyrna_array_contains_py(PointerRNA *ptr, PropertyRNA *prop, PyObject *value)
 
 int pyrna_write_check(void);
 
+void BPY_modules_update(struct bContext *C); //XXX temp solution
+
 #endif