NpgsqlConnectionStringBuilder

NpgsqlConnectionStringBuilder now defaults to protocol version Unknown.
Make sure NpgsqlConnectionStringBuilder never writes "<key>=<empty value>" to a connection string.
Add a constructor NpgsqlConnection(NpgsqlConnectionStringBuilder)
Store password bytes in an encapulation that wipes old password out before storing new one.
Remove most of the defaults; initialize the private fields instead.
Don't put values into base unless they are different from the value default, and also from that type's default value.