Original commit message from CVS:
* gst/videomixer/videomixer.c: (gst_videomixer_reset),
(gst_videomixer_init), (gst_videomixer_query_duration),
(gst_videomixer_query_latency), (gst_videomixer_query),
(gst_videomixer_blend_buffers):
* gst/videomixer/videomixer.h:
Implement position (in time), duration and latency queries.