2.12.8:

* Glib::ObjectBase::is_derived_() is now public, though it is still only for 
  internal use. This allows us to do some optimization of default signal handlers and 
  vfuncs.
  (Armin Burgmeier, Openismus)
* Gtk::Main: Actually do cleanup in the constructor, to allow repeated use and 
  avoid theoretical memory leaks. (Murray Cumming)
  Bug #383340 from Christopher Raine.
* Build:
  - helperlist.h: Avoid warnings about a shadowed member.
  Bug #420316 from Bradley Bell.
  - utility.h: Avoid a warning about a redundant declaration.
  Bug #420339 from Bradley Bell.
* IconTheme::get_example_icon_name() documentation fix.
  (Jonathon Jongsma)