fix by Jie Zhang for exit status and POSIX compliance:

http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
The exit status of a command that terminated because it received a signal shall be reported as greater than 128.

shell/msh.c

@@ -3007,7 +3007,7 @@ static int waitfor(int lastpid, int canintr)
 					prs(" - core dumped");
 				if (rv >= ARRAY_SIZE(signame) || signame[rv])
 					prs("\n");
-				rv = -1;
+				rv |= 0x80;
 			} else
 				rv = WAITVAL(s);
 		}