[cairo] Radial shader transformation

[Thomas Hunger]

> > cairo_save
> >   rotate (Pi/2)
> >  setup_linear_shader ()
> > cairo_restore
> >   rotate  (PI/2)
> >   cairo_rectangle
> >   cairo_fill

This example is bogus since cairo_restore would restore whatever pattern was 
there (e.g. solid, image) right before cairo_save.

   rotate (Pi/2)
  cairo_pattern_linear ()
   rotate  (PI/2)
   cairo_rectangle
   cairo_fill

would work though.

Tom