when upstart init the session jobs, it should be robust against environment changes (fallback?)

A file that is commonly modified is /etc/environment.

If you remove the PATH line in this file, you can start a session upstart-less quite easily, and things will still work.
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"

However, if upstart manage your session, you can't log in (you will be rejected and going back to the greeter quickly). I thnk we should be more fortified against this pebkac issue, especially has we have no really good log for it to know what happened (nothing in lightdm or upstart logs rather than exiting the session and gnome-session logs were not there as it's not executed).

What happens is:
/usr/sbin/lightdm-session: 5: exec: init: not found

in .xsession-errors.

indeed, which init doesn't return anything as /sbin isn't in path. We should maybe hardcode /sbin/init in this script?

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: upstart 1.8-0ubuntu2
ProcVersionSignature: Ubuntu 3.9.0-2.7-generic 3.9.3
Uname: Linux 3.9.0-2-generic x86_64
ApportVersion: 2.10.2-0ubuntu1
Architecture: amd64
Date: Tue May 28 09:51:48 2013
EcryptfsInUse: Yes
InstallationDate: Installed on 2012-05-28 (364 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
SourcePackage: upstart
UpgradeStatus: No upgrade log present (probably fresh install)
UpstartBugCategory: Session
UpstartRunningSessionVersion: init (upstart 1.8)
UpstartRunningSystemVersion: init (upstart 1.8)