Original commit message from CVS:
* gst/videosignal/gstvideodetect.c: (gst_video_detect_420),
(gst_video_detect_set_property), (gst_video_detect_get_property),
(gst_video_detect_class_init):
* gst/videosignal/gstvideodetect.h:
* gst/videosignal/gstvideomark.c: (gst_video_mark_draw_box),
(gst_video_mark_420), (gst_video_mark_set_property),
(gst_video_mark_get_property), (gst_video_mark_class_init):
* gst/videosignal/gstvideomark.h:
Add left and bottom offset properties to control the position of the
pattern.