gtk_css_provider_get_named() is the old GTK3 style API to load themes.
Instead, export the function we currently use,
gtk_css_provider_load_named().
As a side effect we allow people to load a theme as often as they want
without conflicting with GTK's theme.
When loading a per-theme settings.ini file, look for it in
the same directory where we found the gtk.css file for the
theme. Previously, we were always looking in
$prefix/share/themes/THEME/gtk-3.0/, even if the css was
loaded from somewhere else.
https://bugzilla.gnome.org/show_bug.cgi?id=641354
This reverts commit 1f5dea9eba,
since it was causeing noticable behaviour changes.
Previously, GTK_DATA_PREFIX=/ ./gtk3-demo would start
gtk3-demo with the Raleigh theme. With that change, it
was starting with no theme at all (i.e. all black).
