pg_upgrade silently truncates nextMultiOffset to 32 bits

Hi all,
(CCing Heikki as the committer of commit bd8d9c9bdfa)

Commit bd8d9c9bdfa widened MultiXactOffset to uint64, but I found that
pg_upgrade still reads it as a uint32 value when reading the
pg_controldata continents:

else if ((p = strstr(bufin, "Latest checkpoint's NextMultiOffset:")) != NULL)
{
:
p++; /* remove ':' char */
cluster->controldata.chkpnt_nxtmxoff = str2uint(p);

I think it should use strtou64() instead. The attached 0001 patch
fixes it. It introduces str2uint64() as other fields are read by a
similar helper function str2uint().

Also, when checking other similar codes around the new
MultiXactOffset, I found that pg_control_checkpoint() still reports
the value as an xid. I think we should report it as bigint instead.
What do you think? The attached 0002 patch fixes it.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com