hush: make "exit" in trap use pre-trap exitcode - fix for nested trap

function                                             old     new   delta
check_and_run_traps                                  276     278      +2

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-misc/exitcode_trap6.right b/shell/ash_test/ash-misc/exitcode_trap6.right
new file mode 100644
index 0000000..b76c190
--- /dev/null
+++ b/shell/ash_test/ash-misc/exitcode_trap6.right
@@ -0,0 +1,2 @@
+INT
+42:42