histogram example is incorrect

[bkloppenborg]

There are (at least) two issues here with the histogram example:

1. The Perlin distribution should result in a Gaussian-like distribution of noise, whereas the histogram does not display anything remotely close to this, and
2. There appears to be a plotting error wherein every 3n and 4n values are near zero in the histogram.

The Perlin distribution used in the histograms should result in a Gaussian-like noise distribution; however, in the examples, it is anything but Gaussian:

This is even more apparent if one increases the number of bins to around 100:

Also, there appears to be an odd pattern wherein every 3rd and 4th value on the x-axis is near zero.

[9prady9]

@bkloppenborg and @syurkevi I fixed histogram example in api_changes branch. Here are the images.

[9prady9]

I will do similar code changes in CUDA and OpenCL examples.

FYI - These are only changes in example code, the rendering code doesn't have any bugs.