ash,hush: testcase for "exit" without arguments in a trap

hush fails this one

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-misc/exitcode_trap2.right

@@ -0,0 +1 @@
+42:42

shell/ash_test/ash-misc/exitcode_trap2.tests

@@ -0,0 +1,9 @@
+# "exit" in trap should not use last command's exitcode,
+# but exitcode on entering the trap.
+$THIS_SH -c '
+ trap "false;exit" term
+ kill $$ &
+ (exit 42)
+ wait
+'
+echo 42:$?