The scrolling code cannot differentiate between the BUTTON_TOUCHSCREEN post
from normal touches and the one posted in the timeout callback.
To fix introduce a global special button (BUTTON_REDRAW) that results
in the desired redraw. This existed already as a local kludge for android
and is now generalized.
Change-Id: I6bfa6c66431c48f5042fcd8fce2ea72cd3457f58