iPod 3G: Ensure wheel repeats are not generated unless the same keycode is posted...

iPod 3G: Ensure wheel repeats are not generated unless the same keycode is posted more than once in a row, regardless of velocity. Remove 'was_hold' from handle_scroll_wheel calls since the call is never reachable with was_hold being true. Just clear pending ints in one spot after setting levels. Init prev_scroll properly again in 3g case.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27025 a1c6a512-1295-4272-9138-f99709370657