In the 'svnfsfs stats' output, print the size ranges in histograms in a more
user friendly format like "128k .. < 256k" instead of "[2^17..2^18)".

* subversion/svnfsfs/stats-cmd.c
  (print_two_power): New.
  (print_histogram): Call the new function to format size ranges;
                     adjust the format string to accomodate larger sums.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1644037 13f79535-47bb-0310-9956-ffa450edef68