[Patch] checksumming-related buglets in pg_verify_checksums/pg_basebackup TAP tests

Hi,

while hacking on pg_verify_checksums and looking at hexdumps, I noticed
that the TAP tests of pg_verify_checksums (and pg_basebackup from which
it was copy-pasted) actually write "305c305c[...]" (i.e. literal
backslashes and number 0s) instead of "000[...]" into the to-be-
corrupted relfilenodes due to wrong quoting.

This also revealed a second bug in the pg_basebackup test suite where
the offset for the corruption in the second file was wrong, so it
actually never got corrupted, and the tests only passed due to the above
twice than expected number of written bytes. The write() probably
overflowed into an adjacent block so that the total number of corrupted
blocks was as expected by addident. Oops, my bad, patch attached.

Michael

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Michael Banck
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