* wl-summary.el (wl-summary-pick): If call it with prefix

* wl-summary.el (wl-summary-pick): If call it with prefix
argument, set `delete-marks' as non-nil. Pick from only visible
messages.
(wl-summary-check-target-mark): New function.
(wl-summary-target-mark-mark-as-read): Use it.
(wl-summary-target-mark-mark-as-unread): Ditto.
(wl-summary-target-mark-operation): Ditto.
(wl-summary-target-mark-set-flags): Ditto.
(wl-summary-target-mark-save): Ditto.
(wl-summary-target-mark-pick): Ditto.
(wl-summary-target-mark-forward): Ditto.
(wl-summary-target-mark-reply-with-citation): Ditto.
(wl-summary-target-mark-print): Ditto.
(wl-summary-target-mark-uudecode): Ditto.