Added a check on the colormap depth to gdk_drawable_set_colormap()

Added a check on the colormap depth to gdk_drawable_set_colormap()

        * gdk/gdkdraw.c: Added a check on the colormap depth to
        gdk_drawable_set_colormap()
        * gdk/x11/gdkimage-x11.c: combination of Mathias Hasselmann's
        patch to fix colorsel and my patch to fix gdk_drawable_get_image()
        for pixmaps without visuals (more specifically, bitmaps)
        * gdk/x11/gdkpixmap-x11.c: Fixed gdk_pixmap_new() so it
        doesn't set a colormap with the wrong depth