/*
 * call-seq:
 *   post_plugins ["video_filter"|"audio_filter"|"video_vis"|"audio_vis"|"video_compose"] -> array
 *
 * Returns an array of identifiers of all available plugins. If a type is
 * given, the returned array contains only post plugins of the specified type.
 */

static VALUE x_post_plugins(int argc, VALUE *argv, VALUE self) {