unsorted output, to save memory in high-coverage areas

If coverage is very high, glia memory usage can exceed that typically seen for
variant calling.  This occurs because of a streaming sort procedure that
requires holding onto alignments over dag_window_size bases of reference.
Enabling this option will yield output that is unsuitable for variant calling
directly, and should be sorted using e.g. bamtools sort.  However, it should
also decrease the total memory footprint of alignment and variant calling on
the graph.