def get_multi_cas(*keys)
      if block_given?
        get_multi_yielder(keys) {|*args| yield(*args)}
      else
        Hash.new.tap do |hash|
          get_multi_yielder(keys) {|k, data| hash[k] = data}
        end
      end
    end
def get_multi_cas(*keys)
      if block_given?
        get_multi_yielder(keys) {|*args| yield(*args)}
      else
        Hash.new.tap do |hash|
          get_multi_yielder(keys) {|k, data| hash[k] = data}
        end
      end
    end
Fetch multiple keys efficiently, including available metadata such as CAS.
 If a block is given, yields key/data pairs one a time.  Data is an array:
 [value, cas_id]
 If no block is given, returns a hash of
   { 'key' => [value, cas_id] }