* fork.cc (fork_parent): Reinstate "childhProc" protection. Don't close

hProcess handle here since it is used to ensure that a new process isn't
created with the old pid after the old pid exits.
* spawn.cc (spawn_guts): Ditto.
* pinfo.cc (proc_waiter): Don't send any signals if we've execed since this
process doesn't officially exist.
* pinfo.h (pinfo::pid_handle): Eliminate.  Just use hProc.
* sigproc.cc (sig_send): Don't send any signals if our sendsig doesn't exist.
That's a sign that we are execing.
(remove_proc): Eliminate pid_handle close.

winsup/cygwin/pinfo.cc

@@ -742,7 +742,7 @@ proc_waiter (void *arg)
       /* Special case:  If the "child process" that died is us, then we're
 	 execing.  Just call proc_subproc directly and then exit this loop.
 	 We're done here.  */
-      if (hExeced && vchild->pid == myself->pid)
+      if (hExeced)
 	{
 	  /* execing.  no signals available now. */
 	  proc_subproc (PROC_CLEARWAIT, 0);