If the network is down, trying to read blocking will hang the process hard
(ctrl-c not working). Send a cancel signal instead (as suggested in
http://archives.postgresql.org/pgsql-hackers/2012-07/msg00903.php) and go
back into a green polling: this should allow a further error (e.g. another
ctrl-c) to break the loop. In this case we cannot assume anything about
the state of the connection, so we close it.
