Adjust extra lines generated by psql to be valid SQL comments.

Adjust extra lines generated by psql to be valid SQL comments.

psql's --echo-hidden, --log-file, and --single-step options
generate extra lines to clearly separate queries from other output.
Presently, these extra lines are not valid SQL comments, which
makes them a hazard for anyone trying to copy/paste the decorated
queries into a client or query editor.  This commit replaces the
starting and ending asterisks in these extra lines with forward
slashes so that they are valid SQL comments that can be copy/pasted
without incident.

Author: Kirk Wolak
Reviewed-by: Pavel Stehule, Laurenz Albe, Tom Lane, Alvaro Herrera, Andrey Borodin
Discussion: https://postgr.es/m/CACLU5mTFJRJYtbvmZ26txGgmXWQo0hkGhH2o3hEquUPmSbGtBw%40mail.gmail.com