Cast port to integer

Seems that port as string may create problems in PHP 5.3.3 -- http://www.php.net/manual/en/mysqli.construct.php#103521
Cast port to integer

Seems that port as string may create problems in PHP 5.3.3 -- http://www.php.net/manual/en/mysqli.construct.php#103521
Cast port to integer (but not the return value)
Merge pull request #34 from ozh/cast_port

MySQLi: Cast port to integer, just to be safe