In pg_amcheck tests, don't depend on perl's Q/q pack code.

In pg_amcheck tests, don't depend on perl's Q/q pack code.

It does not work on all versions of perl across all platforms.

To avoid endian-ness issues, pick a new value for column a
that has the same upper 4 bytes as lower 4 bytes. Try to
make it something that isn't likely to occur anywhere nearby
in the page.

Discussion: http://postgr.es/m/29DA079B-0658-4E66-BDAA-0EFD7B64D9C6@enterprisedb.com