Allow calling in settings.php

Because of the ordering of the bootstrap, drupal_get_path is not available in settings.php. There are ways around this but being as geoip is likely to be used this early it might be nice to support this.

I'm not sure if this affects d6 yet but this patch allows this functionality in d5.
The one caveat is you'll have to set the variable 'geoip_data_file' either in the conf array for this to work.