Fixed parallel clustering to provide unique cluster ID's

Cluster ID's being generated were not always unique.  Verified new code on job 81348.

# wc -l old/550.cluster.aa90.mapping
552704 old/550.cluster.aa90.mapping
# cut -s -f1 old/550.cluster.aa90.mapping | sort | uniq | wc -l
491524

# wc -l new/550.cluster.aa90.mapping
552704 new/550.cluster.aa90.mapping
# cut -s -f1 new/550.cluster.aa90.mapping | sort | uniq | wc -l
552704