r16274: Fix the smbclient prompting behaviour for both systems that have

r16274: Fix the smbclient prompting behaviour for both systems that have
libreadline and those that don't. We always use the built-in readline
replacement for non-interactive mode. Interactive prompts are always
emitted to stdout and non-interactive mode never prompts at all.

Introduce x_fdup to avoid spuriously closing stdout when a logfile is
specified on the command line and setup_logging is called a second time.
(This used to be commit 848ac756f651a4be231e5635580c0fd5f3d3fa0e)