when bitmask crashes, orphaned polkit process avoids another bitmask launch

Something is wrong with the way we launch the polkit-xxx-authentication agent.

00:02 < micah> micah    12290  0.0  0.0   4320   616 ?        S    17:52   0:00 /bin/sh -c /usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1
00:02 < micah> micah    12291  0.0  0.0 231128  6740 ?        Sl   17:52   0:00 /usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1

(from redmine: created on 2013-08-23, closed on 2013-09-09, relates #3515 (closed))