tracer: use GST_PTR_FORMAT to log the structure
tracer: use GST_PTR_FORMAT to log the structure

This way we only expand the structure when we're logging. This allows us to
meassure the pure tracing seperately from the logging.
Also add some comments on further improvements.

shelsonjava/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer