test: Move cairo_pattern_set_filter to after cairo_set_source_surface

Also update the image.arg32 reference images, since for now we're just
accepting pixman's output as truth.  This fixes up several tests:

                   was   is
 Tests run:        420   420
 Passed:           224   261
 Failed:           195   159
 Expected Failed:  0     0
 Error:            0     0
 Crashed:          0     0
 Untested:         0     0
 Total:            420   420

Thanks to psychon for finding the code error in the test.

test/pixman-downscale.c

@@ -54,9 +54,9 @@ draw (cairo_t *cr, int width, int height, cairo_filter_t filter)
     scale = fmin(x_scale, y_scale);
 
     cairo_save (cr);
-    cairo_pattern_set_filter (cairo_get_source (cr), filter);
     cairo_scale (cr, scale, scale);
     cairo_set_source_surface (cr, image, 0, 0);
+    cairo_pattern_set_filter (cairo_get_source (cr), filter);
     cairo_paint (cr);
     cairo_restore (cr);
     cairo_surface_destroy (image);