activation-helper: Ensure DBUS_STARTER_ADDRESS is set correctly

activation-helper: Ensure DBUS_STARTER_ADDRESS is set correctly

The fix for CVE-2012-3524 filters out all environment variables if
libdbus is used from a setuid program, to prevent various spoofing
attacks.

Unfortunately, the activation helper is a setuid program linking
libdbus, and this creates a regression for launched programs using
DBUS_STARTER_ADDRESS, since it will no longer exist.

Fix this by hardcoding the starter address to the default system bus
address.

Signed-off-by: Geoffrey Thomas <gthomas@mokafive.com>
Signed-off-by: Colin Walters <walters@verbum.org>