Bad preview colormap refcounting in 970925

[Kenneth Albanowski <kjahds kjahds com>]

I'm not at all sure where the source of the problem is, but I'm running
into what is clearly an underref situation with colormaps and
gtk_preview_get_cmap. Specifically, simply saying gdk_colormap_ref(x) and
gdk_colormap_unref(x)  in succession, the color map is apparently deleted.
This is easily demonstrated by adding the colormap_ref/unref calls between
the gtk_preview_get_cmap() and gtk_widget_push_colormap() calls in the
create_color_selection function of testgtk.c.

-- 
Kenneth Albanowski (kjahds@kjahds.com, CIS: 70705,126)