Debugging features for pserialize(9)

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hi,

I implemented two debugging features for pserialize(9):
  http://www.netbsd.org/~ozaki-r/debugging-pserialize.diff

It detects:
- if a context switch happens in a read section, and
- if a sleepable function is called in a read section.

Any comments or suggestions? Is the implementation correct?

Anyway the features have found out two new bugs :)

Thanks,
  ozaki-r