Don't forward SIGINFO to the child when it is send by the kernel

(not another user process).  This is consistent with the handling
of other keyboard-generated signals such as SIGINT, SIGQUIT and
SIGTSTP.  Bug #796

src/exec_nopty.c

@@ -134,6 +134,9 @@ signal_cb_nopty(int signo, int what, void *v)
 	    sudo_ev_loopexit(ec->evbase);
 	}
 	debug_return;
+#ifdef SIGINFO
+    case SIGINFO:
+#endif
     case SIGINT:
     case SIGQUIT:
     case SIGTSTP: