g_dbus_address_connect: specifically use dbus-launch for autolaunch:
g_dbus_address_connect: specifically use dbus-launch for autolaunch:

This only alters what happens if we specifically connect to
"autolaunch:", for instance via "DBUS_SESSION_BUS_ADDRESS=autolaunch:".
We will still potentially try other platform-specific things if
DBUS_SESSION_BUS_ADDRESS is unset. There are currently no other
platform-specific things, so there is no practical difference yet,
but I'm about to add a more-preferred fallback path before autolaunch.

This matches libdbus' behaviour and the D-Bus Specification, in which
the autolaunch: transport specifically means X11 autolaunch
(as implemented by "dbus-launch --autolaunch") on Unix, or a
shared-memory-based protocol on Windows. Other platform-specific
transports or default/fallback modes, including launchd on Mac OS X
and XDG_RUNTIME_DIR/bus on Unix, are not part of "autolaunch:".

It's rather unfortunate that the same name means two different
platform-specific mechanisms, specific to different platforms -
if they were added today I'd call them x11: and windows-shm: or
something - but it's been like this since 2007 so it's too late now.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=747941
Signed-off-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>
Reviewed-by: Philip Withnall <fa619136c81a8d5c7d07f16111b4b9c6c205b678@collabora.co.uk>

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