Denoiser tut fix

I updated both the svn_documentation/tutorial/denoising_454_data.html and the
main tutorial/denoising_454_data.html with the new version after we pulled #654.

I update the main html version, as I think we want to warn users as obvious as possible and not only in the svn documentation. I don't know how many people are actually looking at the svn doc.

Let me know if you disagree.