Hard code freeze break for gnome-themes-standard

[Cosimo Cecchi <cosimoc gnome org>]

Hi,

I made a patch that addresses [1] a glitch in Adwaita. Basically, we
override separator-width for the primary toolbar, to display separators
correctly, so GtkCombobox needs a special case if it's inside a primary
toolbar.

Ok to push?

[1] https://bugzilla.gnome.org/show_bug.cgi?id=646194

Thanks,

Cosimo