mouse wheeling results in fractional zoom levels

[tschaub]

Since r9799, you can unintentionally get fractional zoom levels using the mouse wheel. The easiest way to see this problem is to add a console.log(deltaZ) line to the wheelChange method in the Navigation control (line 213). Alternately, open up an example and use the mouse wheel to zoom just a little bit. Try map.zoom in the console to see numbers like 1.6666666.

The wheelChange method expects an integer deltaZ. The onWheelEvent method in the MousWheel handler does e.detail / 3. I don't see anything that says what to expect for values in the  docs, but I see integer values for detail in FF3.x.

[tschaub]

zoom by integer values

[tschaub]

Navigation control tests continue to pass. Examples like the google one work again.

Thanks for any review.

[bartvde]

Tim, this makes sense to me. Please commit.

[tschaub]

(In [9876]) Only zoom by integer values with changes in the mouse wheel. r=bartvde (closes #2376)