Changes the meaning of CGRP_RELEASABLE to be set on any cgroup that has ever had a task or cgroup in it, or had css_get called on it. The bit is set in cgroup_attach_task, cgroup_create, and __css_get. It is not necessary to set the bit in cgroup_fork, as the task is either in the root cgroup, in which can never be released, or the task it was forked from already set the bit in croup_attach_task. Signed-off-by: Colin Cross <ccross@android.com>