Integrate with GNOME's Recent Documents menu.

Integrate with GNOME's Recent Documents menu.

GTK+ provides GtkRecentManager for this purpose since 2.10. Use it in
wxFileHistory if available. Integration is simple, we just add a file to
GtkRecentManager in addition to normal wxFileHistory handling.

A well-behaved GNOME application would use GtkRecentManager as the
primary store for recent files, so that it reflects when the user works
with supported files in another editor(s) too. But for now, this is much
better than no support at all.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64240 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775