ash,hush: fix "saved" redirected fds still visible in children

Based on a patch by Mark Marshall <mark.marshall@omicronenergy.com>

function                                             old     new   delta
dup_CLOEXEC                                            -      49     +49
fcntl_F_DUPFD                                         46       -     -46

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

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_1.right

@@ -0,0 +1,5 @@
+/proc/self/fd
+/proc/self/fd/0
+/proc/self/fd/1
+/proc/self/fd/2
+/proc/self/fd/3

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_1.tests

@@ -0,0 +1,6 @@
+# The "find" should not see "saved" (duplicated) fd #1
+# Explicitly use bbox find, since other implementations of "find"
+# may open other descriptors as well.
+busybox find /proc/self/fd >tmp_$$.out
+cat tmp_$$.out
+rm -f tmp_$$.out

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_2.right

@@ -0,0 +1,5 @@
+/proc/self/fd
+/proc/self/fd/0
+/proc/self/fd/1
+/proc/self/fd/2
+/proc/self/fd/3

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_2.tests

@@ -0,0 +1,6 @@
+# The "find" should not see "saved" (duplicated) fd #1
+# Explicitly use bbox find, since other implementations of "find"
+# may open other descriptors as well.
+{ busybox find /proc/self/fd; } >tmp_$$.out
+cat tmp_$$.out
+rm -f tmp_$$.out

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_3.right

@@ -0,0 +1,5 @@
+/proc/self/fd
+/proc/self/fd/0
+/proc/self/fd/1
+/proc/self/fd/2
+/proc/self/fd/3

shell/ash_test/ash-redir/redir_children_should_not_see_saved_fd_3.tests

@@ -0,0 +1,6 @@
+# The "find" should not see "saved" (duplicated) fd #1
+# Explicitly use bbox find, since other implementations of "find"
+# may open other descriptors as well.
+{ busybox find /proc/self/fd; true; } >tmp_$$.out
+cat tmp_$$.out
+rm -f tmp_$$.out