pgsql: Handle table_complete_speculative's succeeded argument asdocume

Handle table_complete_speculative's succeeded argument as documented.

For some reason both callsite and the implementation for heapam had
the meaning inverted (i.e. succeeded == true was passed in case of
conflict). That's confusing.

I (Andres) briefly pondered whether it'd be better to rename
table_complete_speculative's argument to 'bool specConflict' or such,
but decided not to. The 'complete' in the function name for me makes
`succeeded` sound a bit better.

Reported-By: Ashwin Agrawal, Melanie Plageman, Heikki Linnakangas
Discussion:
   https://postgr.es/m/CALfoeitk7-TACwYv3hCw45FNPjkA86RfXg4iQ5kAOPhR+F1Y4w@mail.gmail.com
   https://postgr.es/m/97673451-339f-b21e-a781-998d06b1067c@iki.fi

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/aa4b8c61d2cd57b53be03defb04d59b232a0e150

Modified Files
--------------
src/backend/access/heap/heapam_handler.c | 2 +-
src/backend/executor/nodeModifyTable.c   | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)