Update class.MySQL.php

Added a destructor, is needed in case of cleaning up permanent connections
Update class.MySQL.php

Set attributes to private
Added commit and rollback methods;
Added charset management (experimental);
Removed useless setting.
Forces commit before closing.
Update class.MySQL.php

Assume that some fields needs to be public
Correction of mysql_insert_id

the command mysql_insert_id was related to the lastest database
connection
not to the object related one.
Merge pull request #49 from cfilippe/strengthen-transactions

Strengthen transactions