gh-153 Don't (un)serialize the database

This prevents the warning: mysqli_close() [function.mysqli-close]: Couldn't fetch mysqli in /libraries/joomla/database/driver/mysqli.php on line 183

See also:
https://github.com/joomla/joomla-cms/pull/1040
Merge pull request #155 from twentronix/gh-153

gh-153 Don't (un)serialize the database