Update behavior: text can now break lists.

The presence of text below a list item, indented at the same level as or less
than the list item, can now break the list, as the behavior of recent Org-mode
(7.x?). The behavior makes more sense.

I also deleted t/data/listitemclock.org and t/listtimeclock.t submitted by Trent
Fisher. There is nothing clock-related about this, and the new tests for the new
behavior has been included in t/list.t.