2.6.36 introduced the abilitiy to specify the task that is having its
rlimits set.  Update mediation to ensure that confined tasks can only
set their own group_leader as expected by current policy.

Add TODO note about extending policy to support setting other tasks
rlimits.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>