hush: fix EXIT trap recursion case; check redirection failures

function                                             old     new   delta                          
run_pipe                                            1299    1328     +29                          
hush_exit                                             90     102     +12                          
hush_main                                           1172    1179      +7                          
run_list                                            1226    1225      -1                          
------------------------------------------------------------------------------                    
(add/remove: 0/0 grow/shrink: 3/1 up/down: 48/-1)              Total: 47 bytes 

1 files changed, 4 insertions, 0 deletions

diff --git a/shell/hush_test/hush-misc/exit1.tests b/shell/hush_test/hush-misc/exit1.tests
new file mode 100755
index 000000000..41e0d092d
--- /dev/null
+++ b/shell/hush_test/hush-misc/exit1.tests
@@ -0,0 +1,4 @@
+trap "echo Not shown" EXIT
+(exit)  # must be silent
+trap "echo Once; exit" EXIT
+{ exit; }