ext/dvdnav/README: Update the README to use dvddemux

ext/dvdnav/README: Update the README to use dvddemux

Original commit message from CVS:
* ext/dvdnav/README:
Update the README to use dvddemux
* ext/gdk_pixbuf/pixbufscale.c: (gst_pixbufscale_getcaps):
Ensure getcaps returns a subset of the template caps
* gst/mpeg2sub/gstmpeg2subt.c: (gst_mpeg2subt_base_init),
(gst_mpeg2subt_init):
Ensure getcaps returns a subset of the template caps
* gst/mpegstream/gstdvddemux.c: (gst_dvd_demux_class_init),
(gst_dvd_demux_init), (gst_dvd_demux_get_video_stream),
(gst_dvd_demux_get_subpicture_stream),
(gst_dvd_demux_send_subbuffer), (gst_dvd_demux_set_cur_subpicture):
* gst/mpegstream/gstdvddemux.h:
Set the explicit caps on the current_video pad before pushing
anything
* gst/mpegstream/gstmpegdemux.c: (gst_mpeg_demux_get_video_stream),
(gst_mpeg_demux_get_audio_stream):
Free caps used to gst_pad_set_explicit_caps, which takes a const
GstCaps *