Application of patch #5218: patch for bug #9742. Fixes a typo in the

size arg of snprintf(). mhlist output which used to have incorrect lines
such as
     1.2   multipart/mixed            772
     1.21  text/plain                   9
     1.22  multipart/mixed            162
now have the correct
     1.2   multipart/mixed            772
     1.2.1 text/plain                   9
     1.2.2 multipart/mixed            162