threaded, forked, rethreaded processes will deadlock

[Jason Evans]

Brian Fundakowski Feldman wrote:
  > Could you, and anyone else who would care to, check this out?  It's 
a regression
> fix but it also makes the code a little bit clearer.  Thanks!
> 
> Index: lib/libc/stdlib/malloc.c

Why does malloc need to change for this?  Unless there's a really good 
reason, I don't want the extra branches in the locking functions.

Thanks,
Jason