Back in Time release 1.1.20 (fixes a critical bug)

Written for Back In Time by Germar on 2017-04-09

This release fixes a critical bug which could be used to escalate permissions. @mgerstner identified a race condition in Polkit CheckAuthorization. It was reported as CVE-2017-7572 (https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7572)

Changelog:
* backport bug fix: polkit CheckAuthorization: race condition in privilege authorization (https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7572)