use level style compaction
use level style compaction

This seems to be recommended for large (>100G) databases. Also, it looks to be
a tiny bit quicker on bulk load, maybe a few percent. It's hard to tell on a 1
megabase graph though.

ekg/vg,dnanexus-rnd/vg,abeconnelly/vg,ekg/vg,ekg/vg,abeconnelly/vg,dnanexus-rnd/vg