[Merge] lp:~jamesodhunt/upstart/setenv+getenv into lp:upstart

[James Hunt]

Branch updated to only affect a jobs environment by default and to disallow any command that modifies the global environment for PID 1.

Note that this branch is dependent on lp:~jamesodhunt/upstart/remove-basic-user-sessions.

Tests and and update to initctl.8 are still required (follow-on branch).
-- 
https://code.launchpad.net/~jamesodhunt/upstart/setenv+getenv/+merge/142939
Your team Upstart Reviewers is requested to review the proposed merge of lp:~jamesodhunt/upstart/setenv+getenv into lp:upstart.