Miscellaneous PM fixes:

Miscellaneous PM fixes:
o Don't call vm_willexit() more than once upon normal process exit
o Correct two cases of indenting of the no-discussion-possible kind
o Perform slightly stricter ptrace(2) checks:
  - process calling ptrace must be target process's parent
  - process must call wait/waitpid before using ptrace on stopped child
  - no ptrace on zombies
o Allow user processes to use ptrace(T_STOP) to stop an active child