Re: Enable data checksums by default

In general, +1 for $SUBJECT.

     printf(_("  -k, --data-checksums      use data page checksums\n"));
+    printf(_("      --no-data-checksums   do not use data page checksums\n"));

Should we error if both --data-checksum and --no-data-checksums are
specified?  IIUC with 0001, we'll use whichever is specified last.

nitpick: these 4 patches are small enough that they could likely be
combined and committed together.

I think it's fair to say we should make the pg_upgrade experience nicer
once the default changes, but IMHO that needn't block actually changing the
default.

-- 
nathan