code: function _fnVisibleToColumnIndex( oSettings, iMatch )
  	{
  		var aiVis = _fnGetColumns( oSettings, 'bVisible' );
  	
  		return typeof aiVis[iMatch] === 'number' ?
  			aiVis[iMatch] :
  			null;
  	}
docs: Covert the index of a visible column to the index in the data array (take account
  of hidden columns)
  @param {object} oSettings dataTables settings object
  @param {int} iMatch Visible column index to lookup
  @returns {int} i the data index
  @memberof DataTable#oApi