Eliminated detectmod_detect::open_file()

All this function does is call detectmod_detect::open() and writes
metdata. Now write_data() does this.
Modified detecmod_detect::write_data().

This method now uses pulse_data as a data streamer
for .det files. pulse_data::open() opens the file
and writes the metadata header. When unwrapping the
circular buffer, the two chunks are written with
pulse-data::write_chunk().
Cleaned up output of apps/read_det.