Properly reparent traced processes when the tracer dies.

Previously they were uncoditionally reparented to init. In effect
it was possible that tracee was never returned to original parent.

Reviewed by:	kib
MFC after:	1 week
Fix getppid for traced processes.

Traced processes always have the tracer set as the parent.
Utilize proc_realparent to obtain the right process when needed.

Reviewed by:	kib
MFC after:	1 week
The size of the GPT table can not be less than one sector.

Reported by:	rodrigc@
MFC after:	1 week