[Calypso-maint] Bug#865520: calypso: does not listen on IPv6 address

[Roland Hieber]

For the record, an obvious workaround is to put calypso behind a reverse
proxy, for example with nginx:

server {
	listen 80 default_server;
	listen [::]:80 default_server ipv6only=on;
	listen 443 default_server ssl;
	listen [::]:443 default_server ipv6only=on ssl;
# [...]
	location /calendar {
		proxy_set_header Host $host;
		proxy_buffering off;
		proxy_pass https://localhost:5233/calendar;
	}
}

 - Roland