The __ptrace_unlink code that checks for TASK_TRACED fixed the problem of a
thread being left in TASK_TRACED when no longer being ptraced. 

However, an oversight in the original fix made it fail to handle the
case where the child is ptraced by its real parent.

Fixed thus.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>