Revert "Revert "Revert "cgroups: timer_slack: forward port timer_slack to 3.4. http://lwn.net/Articles/431847/"""

This reverts commit bed86ec2c81ebfc278d450bda27688226f00e5cc.
Revert "Revert "kernel: cgroup_timer_slack: Adaptations for 3.4 kernel""

This reverts commit 487dda3195860f1cbe6d200c11fe51bffaacc957.