Commit 453c468737 introduced a use of strerror() into libpq, but that
is not thread-safe. Fix by using strerror_r() instead.
In passing, update some of the code comments added by 453c468737, as
we have learned more about the reason for the change in OpenSSL that
started this.
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: Discussion: https://postgr.es/m/b6fb018b-f05c-4afd-abd3-318c649faf18@highgo.ca
821fbd63ea