function _hash(str){
            var hash = 0, c;
            for (i = 0; i < str.length; i++) {
                c = str.charCodeAt(i);
                hash = c + (hash << 6) + (hash << 16) - hash;
            }
            return hash;
        }
when a table is linked to a infowindow each time a column
is renamed or removed the table pings to infowindow to remove
or rename the fields