gst/avi/avi-ids.h: Add vprp chunk related structures.

gst/avi/avi-ids.h: Add vprp chunk related structures.

Original commit message from CVS:
* gst/avi/avi-ids.h:
Add vprp chunk related structures.
* gst/avi/gstavidemux.c: (gst_avi_demux_riff_parse_vprp),
(gst_avi_demux_parse_stream):
Parse optional vprp chunk and add calculated pixel-aspect-ratio
to caps.  Fixes #539482.
* gst/avi/gstavimux.h:
* gst/avi/gstavimux.c: (gst_avi_mux_pad_reset),
(gst_avi_mux_vidsink_set_caps), (gst_avi_mux_riff_get_avi_header):
Add a vprp chunk if non-trival pixel-aspect-ratio provided in caps.