void set_capacity(std::size_t c)
 {
   auto_space<value_type,Allocator> spc1(spc.get_allocator(),c+1);
   node_impl_type::transfer(begin(),end()+1,spc1.data());
   spc.swap(spc1);
   capacity_=c;
 }
 void reserve(std::size_t c)
 {
   if(c>capacity_){
     auto_space<value_type,Allocator> spc1(spc.get_allocator(),c+1);
     random_access_index_node_impl::transfer(begin(),end()+1,spc1.data());
     spc.swap(spc1);
     capacity_=c;
   }
 }