Fix compilation for glib < 2.23.
Fix compilation for glib < 2.23.

AravisProject/aravis,AravisProject/aravis,lu-zero/aravis,AnilRamachandran/aravis,lu-zero/aravis,AravisProject/aravis,AnilRamachandran/aravis,AnilRamachandran/aravis,AnilRamachandran/aravis,lu-zero/aravis,lu-zero/aravis,AravisProject/aravis,AravisProject/aravis,lu-zero/aravis,AnilRamachandran/aravis