conky-manager fails to build with vala 0.28.0

[heng]

When building the Error

"ListStore' is an ambiguous reference between `GLib.ListStore' and Gtk.ListStore'"

occurs a few times in EditThemeWindow.vala, EditWidgetWindow.vala, SettingsWindow.vala.

[Raphaël Hertzog (hertzog)]

This patch helped to go further but it's not enough to get the package to build on Debian Unstable right now. The next failure is this one:
Main.vala:427.21-427.24: error: Argument 1: Cannot convert from `GLib.CompareFunc<ConkyConfigItem>' to `GLib.CompareDataFunc<ConkyRC>?'
  conkyrc_list.sort(func);
                    ^^^^
Main.vala:476.24-476.27: error: Argument 1: Cannot convert from `GLib.CompareFunc<ConkyConfigItem>' to `GLib.CompareDataFunc<ConkyTheme>?'
  conkytheme_list.sort(func);
                       ^^^^

BTW, I also had to change "--pkg gee-1.0" to "--pkg gee-0.8" because Debian now has dropped support of libgee 0.6 in favor of libgee 0.8 (to follow upstream on this topic: https://wiki.gnome.org/action/show/Projects/Libgee ) Maybe this failure is due to this.