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