gobject: Add helper functions to handle warnings in g_object_new/set/get
gobject: Add helper functions to handle warnings in g_object_new/set/get

g_object_new_is_valid_property
g_object_get_is_valid_property
g_object_set_is_valid_property

https://bugzilla.gnome.org/show_bug.cgi?id=709865

johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib