Implement support for wheel delta with finer resolution than 15 deg.

At the moment, Qt, in many places, does not really understand that
a mouse wheel, or touch pad, might operate on a much higher
granularity than 15 degrees (that is, a delta of 120). This is clear
disadvantage on mac, since the mighty mouse, and track pad, got a
resolution that is close to 1 degree. This is called pixel scrolling.

This patch first and formost changes the implementation of
QAbstractSlider::wheelEvent to _really_ understand what to do when
delta is less than 120. Rather than accumulate delta until 120
is reached, then scroll with a value equal to:
offset * step * QApplication::wheelScrollLines (default = 3), we
multiply offset directly, before waiting for 120. This means that
event tough offset is below 120, multiplying it with wheelScrollLines
and step will very often give a value over 120, menaing we can scroll
much earlier and _much more_ fined grained. This also fixes some
auto tests that was ifdeffed out because of specialised mac code
written inside this function from before.
(NB: we still plan to introduce a new event for pixel scrolling,
perhaps for Qt-4.7)

Rev-By: Andreas
Rev-By: denis

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