code: function __fetchTicketInfo(server, ticketid, callback) {
  
      assert(server.cache_folder);
  
      var filename = server._ticket_cache_file(ticketid);
      //xx console.log("filename " , filename.red);
  
      assert(_.isFunction(callback));
  
      var command = 'issues/' + ticketid.toString() + '.json?include=relations,journals';
  
      perform_http_get_transaction(server,command, function (err, txt) {
  
          txt = fixUnicode(txt);
  
          var ticket = null;
          try {
              var o = JSON.parse(txt);
  
              fs.writeFileSync(filename, JSON.stringify(o, null, " "));
              console.warn(" writing ", filename);
              ticket= o.issue;
          } catch (err) {
              console.log("error !".red, err.message);
              fs.writeFileSync("toto.txt", txt);
              callback(err);
              return;
              // the ticket may have been deleted
          }
          callback(null,ticket);
  
      });
  
  }
docs: \brief extract the full raw information for a given ticket out of redmine
  and store it to a json file in the cache.
  any old version of the ticket json file will be overwritten