added gpu add, subtract, multiply, divide, absdiff with Scalar.

added gpu exp, log, magnitude, based on NPP.
updated setTo with new NPP functions.
minor fix in tests and comments.

modules/gpu/src/beliefpropagation_gpu.cpp

@@ -89,7 +89,7 @@ void cv::gpu::StereoBeliefPropagation::estimateRecommendedParams(int width, int
     int mm = ::max(width, height);
     iters = mm / 100 + 2;
 
-    levels = (int)(log(static_cast<double>(mm)) + 1) * 4 / 5;
+    levels = (int)(::log(static_cast<double>(mm)) + 1) * 4 / 5;
     if (levels == 0) levels++;
 }