sugar-toolkit-gtk3 deprecated functions

[aperezbios]

When compiling sugar-toolkit-gtk3, warnings for the following functions, which are now deprecated, are issued:

gdk_display_get_device_manager is deprecated
gdk_screen_make_display_name is deprecated
gdk_screen_get_number is deprecated
gdk_threads_enter is deprecated
gdk_threads_leave is deprecated
gdk_error_trap_pop is deprecated
gdk_error_trap_pop_ignored is deprecated
gdk_error_trap_push is deprecated
g_type_class_add_private is deprecated

[quozl]

Thanks for testing. Duplicate of #404.