mysqli support

[Dinini]

This has worked for me for the past month with no errors. But I cannot promise this will work fo anyone else. I'm submitting this in case it might help someone else.

wp-settings.php, check for mysqli extension as well as mysql. If mysqli is loaded use the alternate wp-db-mysqli.php file instead of wp-db.php.

wp-includes/wp-db-mysqli.php, only changes from wp-db.php are to convert mysql functions to mysqli functions. The function replacement does not appear to affect the code currently in place.