Switch to -magnification instead of -deltaZ for mac osx pinch-to-zoom

Using pinch-to-zoom in LibreOffice result in following warning in terminal:
soffice[2376:507] -deltaZ is deprecated for NSEventTypeMagnify.  Please use -magnification.

Following https://groups.google.com/a/chromium.org/forum/#!topic/chromium-reviews/lMxCG03aZNs
-deltaZ is deprecated since OSX 10.6. Therefore use -magnification. The forum also
mentions the fact the steps are 500 times smaller. Lets use this factor 500 to keep the
behavior as consistent as possible

Change-Id: Ie769c518492e5b149a5301b19cae8d841047cb22
Reviewed-on: https://gerrit.libreoffice.org/8345Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

vcl/osx/salframeview.mm

@@ -765,11 +765,11 @@ private:
 
         if( bNewSeries )
             mfMagnifyDeltaSum = 0.0;
-        mfMagnifyDeltaSum += [pEvent deltaZ];
+        mfMagnifyDeltaSum += [pEvent magnification];
 
 		mfLastMagnifyTime = [pEvent timestamp];
 		// TODO: change to 0.1 when COMMAND_WHEEL_ZOOM handlers allow finer zooming control
-		static const float fMagnifyFactor = 0.25;
+		static const float fMagnifyFactor = 0.25*500;
         static const float fMinMagnifyStep = 15.0 / fMagnifyFactor;
         if( fabs(mfMagnifyDeltaSum) <= fMinMagnifyStep )
             return;