WL#1031: Fix variables to be consistent

If you get the names from SHOW VARIABLES and try to use them in my.cnf
you will fail is some places:


1) table_type=MYISAM
Config requires to use default_table_type

2) tx_isolation
Config requires to use transaction_isolation
How to repeat:
Just try to start mysqld with option
./mysqld --table_type=MYISAM

[ Noted added 2010-06-15 ]

"1)" is obsolete, we no longer use default_table_type, we use engine.
"2)" is still true.