The xi2 device manager now handles slaves being detached and/or
attached to a master.
gdk_device_list_slaves() has been added so it is possible to
know how slaves relate with masters. The other backends (X11 and not)
don't neeed to to anything special here since their hierarchy is
fully flat.
gdk_enable_multidevice() has been replaced with gdk_disable_multidevice(),
so applications may call that function if they want to go back at the
previous behavior.
There would be usually little reasons to call that function, unless the
application is doing X calls itself that count on old fashioned core
devices.
This function makes a better replacement for
gdk_display_get_core_pointer(), wherever it might yet be needed, for
XI2 resorts to XIGetClientPointer(), for the others return the only
core pointer.
https://bugzilla.gnome.org/show_bug.cgi?id=621685
