Cycles Aperture Ratio - option to produce anamorphic bokeh

Thanks for Aldo Zang for the help with the fix for the panorama/fisheye
depth of field calculation and the overall math.

Reviewed By: sergey, dingto

Subscribers: juicyfruit, gregzaal, #cycles, dingto, matray

Differential Revision: https://developer.blender.org/D753

intern/cycles/render/camera.h

@@ -54,6 +54,9 @@ public:
 	float fisheye_fov;
 	float fisheye_lens;
 
+	/* anamorphic lens bokeh */
+	float aperture_ratio;
+
 	/* sensor */
 	float sensorwidth;
 	float sensorheight;