Debugging function of localcount

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

(resending, please ignore if duplicated)

Hi,

I propose a debugging function of localcount,
localcount_debug_refcnt, which returns a total
reference count of a specified localcount.

A result of localcount_debug_refcnt isn't guaranteed
to be accurate, however it's still useful for
debugging purposes, for example debugging on
ATF tests using rump kernels.

Here is a patch:
  http://www.netbsd.org/~ozaki-r/localcount_debug_refcnt.diff

I added the following assertion in localcount_release:
  KDASSERT(localcount_debug_refcnt(lc) >= 0);

IIUC it's a proper constraint of localcount even if
a result of localcount_debug_refcnt isn't accurate.

Any comments or suggestions?

Thanks,
  ozaki-r