pgsql: amcheck: Reword some messages and fix an alignment problem.

amcheck: Reword some messages and fix an alignment problem.

We don't need to mention the attribute number in these messages, because
there's a dedicated column for that, but we should mention the toast
value ID, because that's really useful for any follow-up troubleshooting
the user wants to do. This also rewords some of the messages to hopefully
read a little better.

Also, use VARATT_EXTERNAL_GET_POINTER in case we're accessing a TOAST
pointer that isn't aligned on a platform that's fussy about alignment,
so that we don't crash while corruption-checking the user's data.

Mark Dilger, reviewed by me.

Discussion: http://postgr.es/m/7D3B9BF6-50D0-4C30-8506-1C1851C7F96F@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9acaf1a62197205b06a85afbfcaa7ffaac939ef3

Modified Files
--------------
contrib/amcheck/verify_heapam.c           | 63 ++++++++++++++++++-------------
src/bin/pg_amcheck/t/004_verify_heapam.pl |  4 +-
2 files changed, 38 insertions(+), 29 deletions(-)