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 

diff --git a/shell/hush_test/hush-misc/redir3.tests b/shell/hush_test/hush-misc/redir3.tests
new file mode 100755
index 0000000..7c28e43
--- /dev/null
+++ b/shell/hush_test/hush-misc/redir3.tests
@@ -0,0 +1,9 @@
+echo Error >/does/not/exist; echo One:$?
+t=BAD
+t=Ok >>/cant/be/created; echo One:$?
+echo $t
+! >/cant/be/created; echo Zero:$?
+exec >/cant/be/created; echo One:$?
+exec /bin/true >/cant/be/created; echo One:$?
+! exec /bin/true >/cant/be/created; echo Zero:$?
+echo Done