Fixes some problems introduced by 6e5f8d489a:
* When reusing conninfo data from the previous connection in \connect,
the host address should only be reused if it was specified as
hostaddr; if it wasn't, then 'host' is resolved afresh. We were
reusing the same IP address, which ignores a possible DNS change
as well as any other addresses that the name resolves to than the
one that was used in the original connection.
* PQhost, PQhostaddr: Don't present user-specified hostaddr when we have
an inet_net_ntop-produced equivalent address. The latter has been
put in canonical format, which is cleaner (so it produces "127.0.0.1"
when given "host=2130706433", for example).
* Document the hostaddr-reusing aspect of \connect.
* Fix some code comments
Author: Fabien Coelho
Reported-by: Noah Misch
Discussion: https://postgr.es/m/20190527203713.GA58392@gust.leadboat.com
313f56ce2d