* signal.cc (_pinfo::kill): Return success on kill(0) only if pid exists or is

in PID_EXITED state.  Report pid 0 when pid does not exist rather than pid -1.
Make debug output reflect actual function call.
* sigproc.cc (stopped_or_terminated): Set process state to reaped when we've
finished waiting for it.
* include/sys/cygwin.h (PID_REAPED): New enum.

winsup/cygwin/include/sys/cygwin.h

@@ -168,7 +168,8 @@ enum
   PID_ALLPIDS	       = 0x02000, /* used by pinfo scanner */
   PID_EXECED	       = 0x04000, /* redirect to original pid info block */
   PID_NOREDIR	       = 0x08000, /* don't redirect if execed */
-  PID_EXITED	       = 0x80000000 /* Free entry. */
+  PID_EXITED	       = 0x40000000, /* Free entry. */
+  PID_REAPED	       = 0x80000000  /* Reaped */
 };
 
 #ifdef WINVER