Don't use hicolor as the default icon-theme
Don't use hicolor as the default icon-theme

The icontheme lookup code has a special-case that prefers builtin icons
if the theme name is "hicolor". This is problematic for our reftests,
which run in a barebones environment with not settings.

davidgumberg/gtk,Sidnioulz/SandboxGtk,Adamovskiy/gtk,jadahl/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,jessevdk/gtk,grubersjoe/adwaita,chergert/gtk,ahodesuka/gtk,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,jessevdk/gtk,ahodesuka/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,alexlarsson/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,chergert/gtk,Adamovskiy/gtk,alexlarsson/gtk,jessevdk/gtk,ahodesuka/gtk,jessevdk/gtk,davidgumberg/gtk,chergert/gtk,chergert/gtk,Adamovskiy/gtk,chergert/gtk,ahodesuka/gtk,ahodesuka/gtk,jadahl/gtk,alexlarsson/gtk,chergert/gtk,grubersjoe/adwaita,jessevdk/gtk,Adamovskiy/gtk,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,jadahl/gtk,jessevdk/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,chergert/gtk,ahodesuka/gtk,chergert/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,Adamovskiy/gtk,jigpu/gtk,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,Lyude/gtk-,grubersjoe/adwaita,jadahl/gtk,ahodesuka/gtk,grubersjoe/adwaita,jadahl/gtk,grubersjoe/adwaita,Lyude/gtk-,ahodesuka/gtk,alexlarsson/gtk,alexlarsson/gtk,Adamovskiy/gtk,Lyude/gtk-,jadahl/gtk,Lyude/gtk-,davidgumberg/gtk,jigpu/gtk