Make pg_controldata report newest XID with valid commit timestamp
Previously pg_controldata didn't report newestCommitTs and this was
an oversight in commit
73c986a.
Also this patch changes pg_resetxlog so that it uses the same sentences
as pg_controldata does, regarding oldestCommitTs and newestCommitTs,
for the sake of consistency.
Back-patch to 9.5 where track_commit_timestamp was added.
Euler Taveira