pgsql: tableam: Add and use table_fetch_row_version().

tableam: Add and use table_fetch_row_version().

This is essentially the tableam version of heapam_fetch(),
i.e. fetching a tuple identified by a tid, performing visibility
checks.

Note that this different from table_index_fetch_tuple(), which is for
index lookups. It therefore has to handle a tid pointing to an earlier
version of a tuple if the AM uses an optimization like heap's HOT. Add
comments to that end.

This commit removes the stats_relation argument from heap_fetch, as
it's been unused for a long time.

Author: Andres Freund
Reviewed-By: Haribabu Kommi
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/9a8ee1dc650be623c32b1df103254847be974d01

Modified Files
--------------
src/backend/access/heap/heapam.c | 9 +----
src/backend/access/heap/heapam_handler.c | 27 ++++++++++++-
src/backend/access/table/tableamapi.c | 1 +
src/backend/commands/trigger.c | 69 ++++++--------------------------
src/backend/executor/execMain.c | 13 ++----
src/backend/executor/nodeModifyTable.c | 22 ++--------
src/backend/executor/nodeTidscan.c | 16 ++------
src/include/access/heapam.h | 2 +-
src/include/access/tableam.h | 43 ++++++++++++++++++--
9 files changed, 91 insertions(+), 111 deletions(-)