download_buffer_automatic_open_target cannot be array anymore
The variable download_buffer_automatic_open_target can no longer be an
array of two targets. This is a reversion from 2009-06-07 back to how it
was before. The behavior of the download-show command is now configured
independently of this variable. To configure download-show, use
set_handler and alternates. The following handlers are provided:
download_show_new_window, download_show_new_buffer,
download_show_new_buffer_background. The default handler of download_show
is alternates(download_show_new_buffer, download_show_new_window).
resolves http://bugs.conkeror.org/issue267