code: function addToQueueCopy(sources, dest, options) {
        if(sources.length === 1) {
          // Simple copy
          queueCopy.push({
            src:      sources[0],
            dest:     dest,
            options:  _.extend({}, options, { realDest: dest, isConcat: false })
          });
        } else {
          // Concat
          sources.forEach(function(src) {
  
            var def       = Q.defer();
            var cacheDest = join(options.cache, fileUID(src));
  
            if(!concatPromises[dest]) {
              concatPromises[dest] = [];
            }
            concatPromises[dest].push(def.promise);
  
            if(!concatSources[dest]) {
              concatSources[dest] = [];
            }
            concatSources[dest].push(cacheDest);
  
            queueCopy.push({
              src:      src,
              dest:     cacheDest,
              options:  _.extend({}, options, { realDest: dest, isConcat: true })
            }, function(err, changed) {
              if(err) {
                return def.reject(err);
              }
              def.resolve(changed);
            });
          });
        }
      }
docs: ------------------------------------------------ 
  Add one or many sources to proceed to destination
  
  @param {Array} sources
  Array of source path
  
  @param {String} dest
  Destination path
  
  @param {Object} options
  Transfo options object
  
  @return {Promise} TODO