Bug#39591: Crash if table comment is longer than 62 characters

It was possible to crash a mysqld build with EXTRA_DEBUG using
CREATE TABLE ... COMMENT with a specially-crafted UTF-8 string.

This CS removes the check that caused it since it no longer
applies in current servers anyway, and adds comments instead
to avoid future confusion. 

mysql-test/r/strict.result:
  Try to crash mysqld with a "suitable" multi-byte (3-byte UTF-8) string
  for a table comment.
mysql-test/t/strict.test:
  Try to crash mysqld with a "suitable" multi-byte (3-byte UTF-8) string
  for a table comment.
sql/unireg.cc:
  Talk at length about limits in .frm form-info, characters vs bytes,
  inlined vs extra-segement TABLE-COMMENTS, and the differences in
  6.0+ vs <6.0 when it comes to UTF-8.
  
  Also, remove a check that no longer applies and that could lead to
  problems in pathological cases.

1 files changed, 7 insertions, 0 deletions

diff --git a/mysql-test/r/strict.result b/mysql-test/r/strict.result
index 34869862a63..c31b5ea2189 100644
--- a/mysql-test/r/strict.result
+++ b/mysql-test/r/strict.result
@@ -1348,6 +1348,13 @@ t1	CREATE TABLE `t1` (
   `i` int(11) default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT='123456789*123456789*123456789*123456789*123456789*123456789*'
 drop table t1;
+CREATE TABLE t3 (f1 INT) COMMENT 'כקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחן';
+SHOW CREATE TABLE t3;
+Table	Create Table
+t3	CREATE TABLE `t3` (
+  `f1` int(11) default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT='כקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחןכקבהחן'
+DROP TABLE t3;
 set sql_mode= 'traditional';
 create table t1(col1 tinyint, col2 tinyint unsigned, 
 col3 smallint, col4 smallint unsigned,