usenet: add -a behavior to config

[Gfy]

Premiumize seems to work with -a, so that server apparently needs that switch. So far, so good. Maybe this can be added as an option in the cfg, so servers, which don't need that switch, won't waste any traffic.

http://rescene.wikidot.com/forum/t-957357/srr-usenet-py#post-2223285