(wl-summary-insert-thread-entity): Search same subject faster. If

(wl-summary-insert-thread-entity): Search same subject faster. If
thread number is reverse, delayed updating thread.
(wl-summary-search-by-subject): Ditto.
(wl-summary-put-alike): Ditto.
(wl-summary-get-alike): Ditto.
(wl-summary-insert-headers): Insert header of all overview in buffer.
(wl-summary-rescan): Delayed updating thread. Kill search subject
buffer for wl-summary-search-by-subject.
(wl-summary-sync-update3): Ditto.
(wl-summary-exit): Ditto.
(wl-summary-goto-bottom-of-current-thread): Change for linked
thread.
(wl-summary-overview-create-summary-line): Change line for linked
thread.

(wl-summary-update-thread): Use wl-thread-maybe-get-children-num.
(wl-summary-set-parent): If change parent, move sub thread.
(wl-summary-redisplay-internal): Add horizontal recenter.
(wl-summary-redisplay-no-mime): Add horizontal recenter.