Gio::Action: Fix API for get_state() and get_state_hint().
Gio::Action: Fix API for get_state() and get_state_hint().

* glib/src/action.hg: get_state() and get_state_hint() now return
a VariantBase instead of void. Bug #690134.

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,johne53/MB3Glibmm,GNOME/glibmm,johne53/MB3Glibmm,johne53/MB3Glibmm,johne53/MB3Glibmm