/*
 * Apply an Imlib2::Filter (eg a static filter)
 *
 * You should probably using Imlib2::Image#filter() instead, since it is
 * polymorphic (eg, it can handle both static and scripted filters).
 * 
 * Example:
 *   filter = Imlib2::Filter.new 20
 *   filter.set 2, 2, Imlib2::Color::GREEN
 *   image.static_filter filter
 *
 */
static VALUE image_static_filter(VALUE self, VALUE filter) {