Fix the bug that a hook may be invoked twice for the same timeline.

* twittering-mode.el: Fix the bug that a hook may be invoked twice
for the same timeline.
(twittering-add-statuses-to-timeline-data): do not invoke a hook
twice for the timeline spec given as `spec'.
Fix the bug that retrieved tweets may not be rendered.
Thanks to irie who reported the problem.

* twittering-mode.el: Fix the bug that retrieved tweets may not be
rendered. This bug is caused by the previous commit. Thanks to
irie who reported the problem.
(twittering-add-statuses-to-timeline-data): call
`twittering-render-timeline' correctly.