add explicit call to System.exit to ensure mem cleanup
improved toString and cosmetics
change metagraph structure : add dag class
serialize metagraph in the end of the dump
fix dag creation in metagraph building
cosmetics
added bfVisit for dags and layer field in metaedges
improved toString
add since and until timestamps to metagraph
added a a copy constructor
Fix to computeTimeLines + no need for oldestTstamp...
fix 'since' initialization
added a static method to build meta-graphs
improved toString
added methods for dag selection (oldest, largest, densier)
bulk upgrade: new meta-graph and sub-graph generation routines