Fail to build with Vala 0.11.2

[Julien Lavergne]

Awn-core fails to build with Vala 0.11.2, with following errors :

labelled-separator.vala:15.5-15.36: error: Private member `TaskManager.LabelledSeparator.child_type' cannot be marked as override, virtual, or abstract
    private override Type child_type ()
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
labelled-separator.vala:20.5-20.38: error: Private member `TaskManager.LabelledSeparator.expose_event' cannot be marked as override, virtual, or abstract
    private override bool expose_event (Gdk.EventExpose event)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Michal Hruby (mhr3)]

This specific issue was fixed, but because of bugs in Vala 0.11.[012] DBus handling, it's not possible to compile Awn. Use valac stable instead until it's fixed.