Fixes for the dark Adwaita GTK+ theme

[Cosimo Cecchi <cosimoc gnome org>]

Hi everyone,

for the last gnome-themes-standard release I introduced a dark variant
in our default GTK+ theme (Adwaita). The dark variant is currently used
by default by at least Totem and Eye of GNOME, which set the
gtk-application-prefer-dark-theme GTK+ setting.
I was not really happy with the result myself, and got some negative
feedback from the RC testers, so I asked Jakub to review the colormap I
used.

Long story short, Jakub tweaked the colormap and the theme SVG assets to
look much, much better, and I integrated them in the patch you can find
here [1]. If there are no objections, I would like to merge this to
gnome-themes-standard master for tomorrow's second release candidate.

[1] http://people.gnome.org/~cosimoc/dark-fix/

Thanks,

Cosimo