This patch fixes strange and obscure pid implementation in current kernels:
- it removes calling of put_task_struct() from detach_pid()
  under tasklist_lock. This allows to use blocking calls
  in security_task_free() hooks (in __put_task_struct()).
- it saves some space = 5*5 ints = 100 bytes in task_struct
- it's smaller and tidy, more straigthforward and doesn't use
  any knowledge about pids using and assignment.
- it removes pid_links and pid_struct doesn't hold reference counters
  on task_struct. instead, new pid_structs and linked altogether and
  only one of them is inserted in hash_list.

Signed-off-by: Kirill Korotaev (kksx@mail.ru)
Signed-off-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>