[HACKERS] wrong t_bits alignment in pageinspect

Hi!

I found out the problem in exposing values of t_bits field from
heap_page_items function.

When the number of attributes in table is multiple of eight, t_bits
column shows double number of bits in which data fields are included.

For example:

# create table tbl(f1 int, f2 int, f3 int, f4 int, f5 int, f6 int, f7
int, f8 int);
# insert into tbl(f1, f8) values (x'f1'::int, 0);

# select t_bits, t_data from heap_page_items(get_raw_page('tbl', 0));

                   t_bits      |       t_data
           ------------------+--------------------
 1000000110001111 | \xf100000000000000

I suppose the prefix 10000001 corresponds to real value of t_bits, the
rest part 10001111 - to the lower byte of f1 field of tbl.

Attached patch fixes this issue.

--
Regards,
Maksim Milyutin