pgsql: Use a more granular approach to follow update chains

Use a more granular approach to follow update chains

Instead of simply checking the KEYS_UPDATED bit, we need to check
whether each lock held on the future version of the tuple conflicts with
the lock we're trying to acquire.

Per bug report #8434 by Tomonari Katsumata

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/4c71f48f4c6c923d1b3f6e6c788e8a0995f4241a

Modified Files
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src/backend/access/heap/heapam.c |  202 ++++++++++++++++++++++++++++++++------
1 file changed, 171 insertions(+), 31 deletions(-)