Original commit message from CVS:
* sys/v4l/gstv4lsrc.c: (gst_v4lsrc_class_init), (gst_v4lsrc_init),
(gst_v4lsrc_fixate), (gst_v4lsrc_query):
* sys/v4l/v4lsrc_calls.c: (gst_v4lsrc_buffer_new):
Fix duration and timestamping, taking latency into account.
Implement latency query.