Re: DB access problem in the first installation step.
I just checked out r951 and I can duplicate this on a vanilla install without integration. I think the problem is with line 80 in db-mysqli.php:
if ( !empty($this->charset) && version_compare(mysql_get_server_info(), '4.1.0', '>=') )
mysql_get_server_info() should be mysqli_get_server_info()
Since the connection was made a couple lines earlier with @mysqli_connect, there is no mysql_connect link identifier, and none is passed in, so line 80 generates a warning and the setting of the charset errors out, and would never happen.
If you add the i to line 80, the warnings go away. I added my comments to the trac ticket.