Modified Files:
   	src/sys/kern: kern_exit.c kern_lwp.c kern_proc.c
   	src/sys/sys: lwp.h proc.h
   
   Log Message:
   Don't free specificdata in lwp_exit2(); it's not safe to block there.
   Instead, free an LWP's specificdata from lwp_exit() (if it is not the
   last LWP) or exit1() (if it is the last LWP).  For consistency, free the
   proc's specificdata from exit1() as well.  Add lwp_finispecific() and
   proc_finispecific() functions to make this more convenient.


hmm, would the problem this fixes have actual symptoms?  i've seen
a couple of crashes with an "alllwp" traversal de-referencing NULL
the last few days and i'm curious if this may be related.