sorting iv files by size

[Seth Teller <teller@lcs.mit.edu>]

for debugging purposes, it can be useful to
validate iv files in order from small to
large, i.e., using

  % cd /scratch/willtor_extrude_MIT/willtor_new_run/test_run2/
  % ls -l */3D.iv | sort -n +5 > /tmp/foo

then the file /tmp/foo has smallest files first.