message: Update documentation for cv::accumulate.
  Make it more clear for the type of input argument.
diff: @@ -2588,9 +2588,8 @@ The function supports multi-channel images. Each channel is processed independen
  The functions accumulate\* can be used, for example, to collect statistics of a scene background
  viewed by a still camera and for the further foreground-background segmentation.
  -@param src Input image as 1- or 3-channel, 8-bit or 32-bit floating point.
  -@param dst %Accumulator image with the same number of channels as input image, 32-bit or 64-bit
  -floating-point.
  +@param src Input image of type CV_8UC(n), CV_16UC(n), CV_32FC(n) or CV_64FC(n), where n is a positive integer.
  +@param dst %Accumulator image with the same number of channels as input image, and a depth of CV_32F or CV_64F.
  @param mask Optional operation mask.
  @sa accumulateSquare, accumulateProduct, accumulateWeighted
  