debian/NEWS: fixing default SSL/TLS behavior description

Thanks to Ralf Jung, Filipus Klutiero, and kiki coco for some
suggestions and corrections.

Closes: #768118
debian/NEWS: adding notes around new security changes

As Mozilla has dropped the SSL 3.0 support and implement a setting for
TLS protocal version fall backs adding some infos around this into
debian/NEWS and debian/README.Debian.