Mail Folder Analyzer Revisited

Now that we've sped up the analyzer by a factor of 6, let's see what else we can do
We'll rerun the test under the profiler

     % perl -d:DProf mfa2.pl MBOX  > /dev/null
     % dprofpp

     Total Elapsed Time = 1.492102 Seconds
       User+System Time = 1.302102 Seconds
     Exclusive Times
     %Time ExclSec CumulS #Calls sec/call Csec/c  Name
      63.7   0.830  0.829    109   0.0076 0.0076  main::letter_histogram
      13.8   0.180  0.180      1   0.1800 0.1800  Mail::Util::read_mbox
      4.61   0.060  0.130      3   0.0200 0.0432  main::BEGIN
      4.61   0.060  0.887    109   0.0005 0.0081  main::handle_message
      2.30   0.030  0.030      1   0.0300 0.0300  warnings::BEGIN
      2.30   0.030  0.040      5   0.0060 0.0080  Mail::Util::BEGIN
      0.77   0.010  0.010      3   0.0033 0.0033  AutoLoader::BEGIN
      0.77   0.010  0.010      2   0.0050 0.0050  main::pairify
      0.77   0.010  0.010      4   0.0025 0.0025  vars::BEGIN
      0.00   0.000 -0.000      3   0.0000      -  strict::import
      0.00   0.000 -0.000      3   0.0000      -  strict::bits
      0.00   0.000 -0.000      2   0.0000      -  Exporter::import
      0.00   0.000 -0.000      1   0.0000      -  warnings::import
      0.00   0.000 -0.000      1   0.0000      -  warnings::register::import
      0.00   0.000 -0.000      2   0.0000      -  warnings::register::mkMask

We see that letter_histogram is run 109 times at 7.6 ms each
- This is 64% of the remaining run time