Save a few bytes per CatCTup

Hi,

The current code in CatalogCacheCreateEntry():

```
ct = (CatCTup *) palloc(sizeof(CatCTup) +
MAXIMUM_ALIGNOF + dtp->t_len);
ct->tuple.t_len = dtp->t_len;
ct->tuple.t_self = dtp->t_self;
ct->tuple.t_tableOid = dtp->t_tableOid;
ct->tuple.t_data = (HeapTupleHeader)
MAXALIGN(((char *) ct) + sizeof(CatCTup));
/* copy tuple contents */
memcpy((char *) ct->tuple.t_data,
(const char *) dtp->t_data,
dtp->t_len);
```

If I understand correctly, we just want "ct->tuple.t_data" align
to MAXIMUM_ALIGNOF here. So we can save MAXIMUM_ALIGNOF
bytes per CatCTup by this:

```
ct = (CatCTup *) palloc(MAXALIGN(sizeof(CatCTup)) +
dtp->t_len);
ct->tuple.t_len = dtp->t_len;
ct->tuple.t_self = dtp->t_self;
ct->tuple.t_tableOid = dtp->t_tableOid;
ct->tuple.t_data = (HeapTupleHeader)
(((char *) ct) + MAXALIGN(sizeof(CatCTup)));
/* copy tuple contents */
memcpy((char *) ct->tuple.t_data,
(const char *) dtp->t_data,
dtp->t_len);
```

It's correct because palloc() always return a max-aligned pointer.

--
Regards,
ChangAo Chen