Several fixes to array handling in ecpg.

Patches by Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Add missing include.

This is more cleanup from commit 11a65eed1637a05b03e174700799b024e104bfb4.

Amit Kapila
Fix misc typos in comments.
docs:  add link to pg_start_backup() from pg_basebackup --checkpoint

This references the meaning of the fast/spread checkpoint option.

Per private IM report
Fix a few more misc typos in comments.
Fix typo in comment.

Tomonari Katsumata
C comment:  track_activity_query_size doesn't support memory units

And explain why.

Per report from Pavel Stehule