hush: fix stdin of backgrounded pipe

function                                             old     new   delta
run_list                                            2450    2502     +52

shell/hush_test/hush-misc/redir5.right

@@ -0,0 +1,4 @@
+Backgrounded pipes shall have their stdin redirected to /dev/null
+Zero:0
+Zero:0
+Done

shell/hush_test/hush-misc/redir5.tests

@@ -0,0 +1,13 @@
+echo "Backgrounded pipes shall have their stdin redirected to /dev/null"
+
+# 1. bash does not redirect stdin to /dev/null if it is interactive.
+# hush does it always (this is allowed by standards).
+
+# 2. Failure will result in this script hanging
+
+cat & wait; echo Zero:$?
+
+# This does not work for bash! bash bug?
+cat | cat & wait; echo Zero:$?
+
+echo Done