list_browser ->next_line: [int]Move forward by arg lines. If an incremental search is in progress,
moves it moves the current search to the next line. If the current
search pattern does not match the new item, it is set to the entire next
item. If there is no search in progress, the browsercan only select a
single object (list_browser->multiple_selection: @off)
and the selection is in the visible part of the browser, the selected
object is taken as the start of the search. Otherwise, the top of the
visible page is choosen.
list_browser->previous_line
simply negates the argument before calling
list_browser->next_line.
