Replace `sit-for' with `sleep-for' for avoiding an infinite loop.

* twittering-mode.el: Replace `sit-for' with `sleep-for' for
avoiding an infinite loop. On rare occasions, `sit-for' may return
immediately even when no input is available (See the document of
`input-pending-p'). Since Emacs does not update status of an
asynchronous process in those cases, a loop which uses `sit-for'
and waits for a finish of a process will wait infinitely. To avoid
the situation, invocations of `sit-for' are replaced with those of
`sleep-for'. Thanks to Ikumi Keita, who investigates the problem
and writes this patch.
(twittering-wait-while): use `sleep-for' instead of `sit-for'.
(twittering-oauth-get-token-alist-url): likewise.