ash: fix $! value when traps are set

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-trap/signal7.right b/shell/hush_test/hush-trap/signal7.right
new file mode 100644
index 0000000..ba7453e
--- /dev/null
+++ b/shell/hush_test/hush-trap/signal7.right
@@ -0,0 +1 @@
+Bug detected: 0