Catch up to r325719 which makes the kern.proc.pid sysctl "work" for zombies.

Catch up to r325719 which makes the kern.proc.pid sysctl "work" for zombies.

Some of the ptrace tests need to wait for a child process to become a
zombie before preceding.  The parent process polls the child process
via the kern.proc.pid sysctl to wait for it to become a zombie.
Previously the code polled until the sysctl failed with ESRCH.  Now it
will poll until either the sysctl fails with ESRCH (for compatiblity
with older kernels) or returns a kinfo_proc structure with the ki_stat
field set to SZOMB.

Reported by:	Jenkins
Tested by:	markj
Discussed with:	mjg
MFC after:	1 week