configure: disable the defaults service if PolicyKit is not available
configure: disable the defaults service if PolicyKit is not available

The enable_defaults_service is set to "auto" by default, but needs to be
set to "no" if PolicyKit is not found.

GNOME/gconf,GNOME/gconf,GNOME/gconf,Distrotech/GConf,Distrotech/GConf,Distrotech/GConf,hyperair/gconf-gdbus,hyperair/gconf-gdbus,Distrotech/GConf,GNOME/gconf,hyperair/gconf-gdbus,hyperair/gconf-gdbus