Prepare for 5.x where HA_READ_PREFIX_LAST may pass only a few first bytes of the last field in a key value
ha_innodb.cc:
  In 4.0 always assume HA_READ_PREFIX_LAST passes a complete-field prefix of a key value; LIKE queries use a padding trick


sql/ha_innodb.cc:
  In 4.0 always assume HA_READ_PREFIX_LAST passes a complete-field prefix of a key value; LIKE queries use a padding trick
innobase/page/page0cur.c:
  Prepare for 5.x where HA_READ_PREFIX_LAST may pass only a few first bytes of the last field in a key value