nitrogen tissue saturation toggle is broken

[Salvo Tomaselli]

> I was wondering about your build problems. With the latest master you should be able to simply compile from source.
Oh I thought I had replied.
Problem 1: there is no URL on the website that I can give to git
clone. I am stuck at this step.

This page http://subsurface-divelog.org/it/download/ links to a web
interface. But it is unclear how to get a local git repo.

> What am I missing?
Well Initially I just had the tissue, without the ceiling, then
toggled them, and now I can't have the tissues without the ceiling
anymore.