* wl.el (wl-check-variables-2): Don't check wl-summary-line-format

* wl.el (wl-check-variables-2): Don't check wl-summary-line-format
and wl-folder-summary-line-format.

* wl-summary.el (wl-summary-message-visible-p): New inline function.
(wl-summary-put-temp-mark): Rename from wl-summary-mark-line.
(wl-summary-set-score-mark): Use it.
(wl-summary-target-mark-mark-as-read): Ditto.
(wl-summary-target-mark-mark-as-unread): Ditto.
(wl-summary-target-mark-mark-as-important): Ditto.
(wl-summary-target-mark-msgs): Simplified.
(wl-summary-detect-mark-position): Fixed problem when
summary-line-format no contain persisten/temp mark spec.
(wl-summary-temp-mark): Ditto.
(wl-summary-persistent-mark): Ditto.
(wl-summary-update-persistent-mark): Ditto.

* wl-action.el (wl-summary-set-mark): Ditto.
(wl-summary-unset-mark): Ditto.
All other related portions are changed.