(4.1 version, with post-review fixes)
  
  The fix for another Bug (6439) limited FROM_UNIXTIME() to
  TIMESTAMP_MAX_VALUE which is 2145916799 or 2037-12-01 23:59:59 GMT,
  however unix timestamp in general is not considered to be limited 
  by this value. All dates up to power(2,31)-1 are valid.
  
  This patch extends allowed TIMESTAMP range so, that max
  TIMESTAMP value is power(2,31)-1. It also corrects
  FROM_UNIXTIME() and UNIX_TIMESTAMP() functions, so that
  max allowed UNIX_TIMESTAMP() is power(2,31)-1. FROM_UNIXTIME()
  is fixed accordingly to allow conversion of dates up to
  2038-01-19 03:14:07 UTC. The patch also fixes CONVERT_TZ()
  function to allow extended range of dates.
  
  The main problem solved in the patch is possible overflows
  of variables, used in broken-time representation to time_t
  conversion (required for UNIX_TIMESTAMP).