Added sampling of trait frequencies, recording this to the database.  Two existing bugs need attention:  tree shapes r=6, h=3 cause a fatal exception with trait ID's not in the union trait graph.  And trait frequencies don't mean much, they're individually the proportion of the population size that has the trait.  So calculating the evenness doesn't seem to mean much since it's not a closed array of frequencies.
Fixed issue with population initialization; had to move away from the calculation of node indices, to walking edges down from the root.  This prevents any "not in graph" issues.