As an addition to 1042372670, themes might
want to avoid using the hardcoded GTK defaults for legacy GtkStyle
values. Add a gtkstyle-fallback style class that can be used by themes
to tweak the legacy GtkStyle defaults.
https://bugzilla.gnome.org/show_bug.cgi?id=679092
We can't expose colors with alpha in the GtkStyle colors, since
GdkColor has no alpha. Currently we throw away alpha completely,
which fails very badly for completely transparent backgrounds,
which now is the default for most widgets, as it typically
end up with black-on-black.
We handle this by falling back on the default/previous colors for
transparent colors. This is is simple and avoids complete failure.
https://bugzilla.gnome.org/show_bug.cgi?id=671437
