code: function(bgp, toJoin, newGroups, newGroupVars) {
          var acumGroups = [];
          var acumId = "";
          var acumVars = "";
          for(var gid in toJoin) {
              acumId = acumId+gid; // new group id
              acumGroups = acumGroups.concat(groups[gid]);
              acumVars = acumVars + groupVars[gid]; // @todo bug here? we were not adding...
          }
  
          acumVars = acumVars + vars.join("/") + "/";
          acumGroups.push(bgp);
  
          newGroups[acumId] = acumGroups;
          newGroupVars[acumId] = acumVars;
      }
docs: Creates a new group merging the vars and the groups