The current way of exposing GDK API that should be considered internal
to GTK+ is to append a 'libgtk_only' suffix to the function name; this
is not really safe.
GLib has been using a slightly different approach: a private table of
function pointers, and a macro that allows accessing the desired symbol
inside that vtable.
We can copy the approach, and deprecate the 'libgtk_only' symbols in
lieu of outright removal.
https://bugzilla.gnome.org/show_bug.cgi?id=739781
This patch changes all uses of GDK_DEPRECATED(_FOR) in gdk headers
by the versioned variants, GDK_DEPRECATED_IN_3_x(_FOR). At the same
time, we add GDK_AVAILABLE_IN_3_x annotations for all API additions
in 3.2 and 3.4.
This commit hides the GdkDisplayManager instance and class structs,
adds vfuncs for listing displays, opening displays, and getting and
setting the default display. The X11 backend has a derived
GdkDisplayManagerX11.
The gdk_display_manager_get() function is responsible for deciding on
which of the compiled in backends to use. Currently, it consults the
GDK_BACKEND environment variable and falls back to x11.
