D-Bus backend: Add GCONF_DEFAULT_SOURCE_PATH support (#664031)
D-Bus backend: Add GCONF_DEFAULT_SOURCE_PATH support (#664031)

Forward-port 7baf4c6b33a6dd0697a8bdb81bd86c72d58ebdc6
("Allow overriding the default config via $GCONF_DEFAULT_SOURCE_PATH")
from the ORBit to the D-Bus backend to fix (sugar-)jhbuild breakage when
building with --disable-orbit.

GNOME/gconf,hyperair/gconf-gdbus,hyperair/gconf-gdbus,GNOME/gconf,hyperair/gconf-gdbus,GNOME/gconf,GNOME/gconf,hyperair/gconf-gdbus