We should consider whether the selected Thread is within the same jail
or not.
Therefore let's make it clear to callers with jail semantics if a called
method checks if the desired Thread object is within the same jail.
As for Thread::for_each_* methods, currently nothing in the kernel
codebase needs iteration with consideration for jails, so the old
Thread::for_each* were simply renamed to include "ignoring_jails" suffix
in their names.
cbaa3465a8