Log Message:
Changes 2.6.3:
* Gtk::Action::get_proxies()
  Use the correct ownership semantics.
* Gdk::Display::list_devices()
  Use the correct ownership semantics.
* examples/book/menus_and_toolbars/
  Distribute the .png file.

Changes 2.6.2:
* TreeView: When using the append_column() convenience API,
  prevent a crash when the window closes while the cell is
  editing.
* Allow derived CellRenderers to be edited, by removing
  some debug code that sneaked into 2.6.1.
* Documented many signals, based on the GTK+ documentation.

Changes 2.6.1:
* CellRenderer: Prevent an infinite loop.
* MSVC++ .Net 2003 build fixes.
* Documentation:
  - Hide deprecated widgets from the list of widgets.
  - Correct the description of the IO input example.

Chamges 2.6.0:
gtkmm 2.6 wraps new API in GTK+ 2.6, and is API/ABI-compatibile with gtkmm 2.4.