ash: hopefully close bug 4324. With testcase.

function                                             old     new   delta
evaltree                                             621     869    +248
popstring                                            134     140      +6

shell/ash_test/ash-signals/signal2.right

@@ -0,0 +1,3 @@
+sleeping
+child exits as expected
+parent exits

shell/ash_test/ash-signals/signal2.tests

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+$THIS_SH -c '
+cleanup() {
+    echo "child exits as expected"
+    exit
+}
+trap cleanup HUP
+echo "sleeping"
+sleep 1
+echo "BAD exit from child!"
+' &
+
+child=$!
+sleep 0.1 # let child install handler first
+kill -HUP $child
+wait
+echo "parent exits"