Thanks to Martin Friebe for finding and submitting a fix for this bug!
  
  A table with maximum number of key segments and maximum length key name
  would have a corrupted .frm file, due to an incorrect calculation of the
  complete key length.  Now the key length is computed correctly (I hope) :-)
  
  MyISAM would reject a table with the maximum number of keys and the maximum
  number of key segments in all keys.  It would allow one less than this total
  maximum.  Now MyISAM accepts a table defined with the maximum.  (This is a
  very minor issue.)