Weak-pointers are currently lacking g_set_object() & g_clear_object()
helpers equivalent. New functions (and macros, both are provided) are
convenient in many case, especially for the property's notify-on-set
pattern:
if (g_set_weak_pointer (...))
g_object_notify (...)
Inspired by Christian Hergert's original implementation for
gnome-builder.
https://bugzilla.gnome.org/show_bug.cgi?id=749527
156d32cb80