modify getattr stats to read-only and config's file size
add ..pids special file that appears when one or more readers exist
refactor readClusteredFile, various updates for cluster flow

add tree of functions called from readClusteredFile, mostly pseudocode for now:
  readClusteredFile -> fillClusterQueues +-> fileClusterQueues
                                         \-> parsePackets -> getFreeLink
added or enhanced course-grained locking around access to instance, residual, and cluster arrays
moved readQueu blocking mutex from static scope to cluster structure (per cluster)
added several checks to acesses of cluster->instance[i] to avoid segvs when instances are completing
removed several unneeded debug statements to unclutter output
added checks for release callback to set flags in remaining cluster members when one quits