Fix a compile failure in the mpeg2new plugin.
Use macros for the aspect ratio numbers.

diff --git a/src/libmpeg2new/xine_mpeg2new_decoder.c b/src/libmpeg2new/xine_mpeg2new_decoder.c
--- a/src/libmpeg2new/xine_mpeg2new_decoder.c
+++ b/src/libmpeg2new/xine_mpeg2new_decoder.c
@@ -153,18 +153,17 @@ static void mpeg2_video_decode_data (vid
         _x_stream_info_set(this->stream, XINE_STREAM_INFO_VIDEO_WIDTH,     info->sequence->picture_width);
         _x_stream_info_set(this->stream, XINE_STREAM_INFO_VIDEO_HEIGHT,    info->sequence->picture_height);
         _x_stream_info_set(this->stream, XINE_STREAM_INFO_FRAME_DURATION,  info->sequence->frame_period / 300);
-        if (this->force_aspect) info->sequence->pixel_width = this->force_aspect;
-        switch (info->sequence->pixel_width) {
-	case 3:
+        switch (this->force_aspect ? this->force_aspect : info->sequence->pixel_width) {
+	case XINE_VO_ASPECT_ANAMORPHIC:
 	  this->ratio = 16.0 / 9.0;
 	  break;
-	case 4:
+	case XINE_VO_ASPECT_DVB:
 	  this->ratio = 2.11;
 	  break;
-	case 2:
+	case XINE_VO_ASPECT_4_3:
 	  this->ratio = 4.0 / 3.0;
 	  break;
-	case 1:
+	case XINE_VO_ASPECT_SQUARE:
 	default:
 	  this->ratio = (double)info->sequence->picture_width/(double)info->sequence->picture_height;
 	  break;