function _fnDataSource(settings) {
		if (settings.oFeatures.bServerSide) {
			return 'ssp';
		}
		else if (settings.ajax) {
			return 'ajax';
		}
		return 'dom';
	}
Detect the data source being used for the table. Used to simplify the code
a little (ajax) and to make it compress a little smaller.

 @param {object} settings dataTables settings object
 @returns {string} Data source
 @memberof DataTable#oApi