parent.
* dcrt0.cc (do_exit): Don't cleanup pinfo on exit. That happens automatically
now.
* exceptions.cc (signal_exit): Ditto.
* fork.cc (fork_parent): Use stack_here value passed in from fork().
(fork): Figure out top of stack here and pass it to fork_parent.
* pinfo.cc (_pinfo::record_death): Eliminate.
* pinfo.h (_pinfo): Ditto.
* sigproc.cc (proc_exists): Simplify.
(proc_terminate): Ditto.
(remove_zombie): Don't cleanup pinfo stuff.
(wait_sig): Send subproc_ready signal whether execed or spawned.
* spawn.cc (spawn_guts): Always create subproc_ready event. Use it for both
exec and spawn.
(_spawnve): Send proper mode to spawn_guts when mode != _P_OVERLAY.