ash: add slightly different testcase

shell/ash_test/ash-signals/signal3.tests

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+$THIS_SH -c '
+hup() {
+    echo "child got HUP"
+}
+trap hup HUP
+echo "child sleeps"
+sleep 1
+echo "child exits"
+' &
+
+child=$!
+sleep 0.1 # let child install handler first
+kill -HUP $child
+wait
+echo "parent exits"