fix subtitles position (aspect ratio)

the subtitle was displayed fine but since aspect ratios didn't match it
wasn't positioned correctly on the vout. ie:
--------------
|            |
|            |
|      subtit|
|            |
-------------- ( http://people.videolan.org/~dionoea/vlcsubs.png )

now it's displayed in the center but the letters are scaled horrizontaly
(which doesn't look too good ... but at least everything is displayed)
( http://people.videolan.org/~dionoea/vlcsubs2.png )

modules/codec/dvbsub.c

@@ -1387,7 +1387,10 @@ static subpicture_t *render( decoder_t *p_dec )
         /* Create new SPU region */
         memset( &fmt, 0, sizeof(video_format_t) );
         fmt.i_chroma = VLC_FOURCC('Y','U','V','P');
-        fmt.i_aspect = 0; /* 0 means use aspect ratio of background video */
+        /* FIXME -> subtitles will be squished when using VOUT_ASPECT_FACTOR
+           and they won't be placed correctly when using 0 and the video's
+           aspect ratio is different than the vout's aspect ratio */
+        fmt.i_aspect = VOUT_ASPECT_FACTOR;
         fmt.i_width = fmt.i_visible_width = p_region->i_width;
         fmt.i_height = fmt.i_visible_height = p_region->i_height;
         fmt.i_x_offset = fmt.i_y_offset = 0;