improve graph indexing + kmer indexing performance
improve graph indexing + kmer indexing performance

Compact only once after we've got kmers in the graph, rather than doing paths
after kmers and compacting twice.

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