Display InsecureRequestWarning only once per server

[tkzv]

When I download a gallery anonymously using a dubious proxy, I sometimes get certificate errors. That's OK, if I'm not sending anything confidential, so I use --no-check-certificate switch. This way I get warnings for every file I download.

I don't want to disable those warnings completely, they may carry some information. But the way it is currently done, redundant warnings drown out the relevant ones.

Please, add a switch to display warnings only once per host, rather than for each file.

[mikf]

Done in commit eb68d45.

It now only shows an InsecureRequestWarning once per domain, and you can configure this behavior with a global warnings option.