A small problem when rehashing catalog cache

[cca5507]

Hi,

When we search catalog cache, we move the searched tuple to the front of the 
list:

```
                /*
                 * We found a match in the cache.  Move it to the front of the 
list
                 * for its hashbucket, in order to speed subsequent searches.  
(The
                 * most frequently accessed elements in any hashbucket will 
tend to be
                 * near the front of the hashbucket's list.)
                 */
                dlist_move_head(bucket, &ct->cache_elem);
```

If I understand correctly, we reverse the list in RehashCatCache() and 
RehashCatCacheLists():

```
        /* Move all entries from old hash table to new. */
        for (i = 0; i < cp->cc_nbuckets; i++)
        {
                dlist_mutable_iter iter;

                dlist_foreach_modify(iter, &cp->cc_bucket[i])
                {
                        CatCTup    *ct = dlist_container(CatCTup, cache_elem, 
iter.cur);
                        int                     hashIndex = 
HASH_INDEX(ct->hash_value, newnbuckets);

                        dlist_delete(iter.cur);
                        dlist_push_head(&newbucket[hashIndex], &ct->cache_elem);
                }
        }
```

Maybe "dlist_push_head" -> "dlist_push_tail"? Thoughts?

--
Regards,
ChangAo Chen