adding support for port parameter for the database

mysqli passes the port in as a parameter versus mysql_connect()'s method of using the hostname http://localhost:8889. http://www.php.net/manual/en/mysqli.construct.php This change will allow you to specify a port in the config that gets used when setting up the connection. I found it useful when utilizing this with MAMP when the default port is 8889 for MySQL.

It can be set just like the other config settings by executing:
./bin/config set mysql.port 8889

Related libphutil change to support ports: https://github.com/facebook/libphutil/pull/27