TABLES IN INCORRECT ENGINE

PROBLEM:
  CREATE/ALTER TABLE currently can move system tables like
mysql.db, user, host etc, to engines other than MyISAM. This is not
completely supported as of now, by mysqld. When some of system tables
like plugin, servers, event, func, *_priv, time_zone* are moved
to innodb, mysqld restart crashes. Currently system tables
can be moved to BLACKHOLE also!!!.

ANALYSIS:
  The problem is that there is no check before creating or moving
a system table to some particular engine.

  System tables are suppose to be residing in MyISAM. We can think
of restricting system tables to exist only in MyISAM. But, there could
be future needs of these system tables to be part of other engines
by design. For eg, NDB cluster expects some tables to be on innodb
or ndb engine. This calls for a solution, by which system
tables can be supported by any desired engine, with minimal effort.

FIX:
  The solution provides a handlerton interface using which,
mysqld server can query particular storage engine handlerton for
system tables that it supports. This way each storage engine
layer can define their own system database and system tables.

  The check_engine() function uses the new handlerton function
ha_check_if_supported_system_table() to check if db.tablename
provided in the DDL is supported by the SE.

Note: This fix has modified a test in help.test, which was moving
mysql.help_* to innodb. The primary intention of the test was not
to move them between engines.