Used the same style as existing code, added a new virtual isMinOrMax()
and add some special casing in Reduction::GenSlidingWindowFunction(),
and fsim_count() and fmax_count() functions that count how many
non-NaN numbers we actually see. As such, I am not sure at all that
this is an ideal way to do this, but will have to do for now.

Change-Id: I846a8d24f4563f8fae1a45971a4ce202ed918487
Signed-off-by: Michael Meeks <michael.meeks@collabora.com>