ash: trap with bad signal name should not abort

function                                             old     new   delta
trapcmd                                              236     271     +35

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-signals/signal4.right b/shell/ash_test/ash-signals/signal4.right
new file mode 100644
index 0000000..3260584
--- /dev/null
+++ b/shell/ash_test/ash-signals/signal4.right
@@ -0,0 +1,4 @@
+./signal4.tests: trap: line 3: BADNAME: invalid signal specification
+1
+Trapped
+Ok