no anerobic digester after researching wastewater treatment

Issue description

as the title says, I just researched wastewater treatment, and I can't find the digester building... notice how it's locked here

also, the building can't be found in the menus below. when clicking on the lock, it shows me this:

(additionally, notice that the toxic slurry recipe exists, when it shouldn't)

Reproduction steps

1. load save
2. observe how there's no digester to process sludge

Game version and build number

v0.6.4c (b341)

Operating system

Windows

Attachments

trying to build wastewater: bug - no digester.save
right before the research finishes: bug - just before.save

actually, I just realised that I it's probably because I don't have biodiesel researched... dang, well still a bug nonetheless

also, is there a way that I can contribute a script (or C# code) which walks the research tree and ensures:

1. the machine is available when the recipe is unlocked
2. the recipe is unlocked when the material is unlocked (for example veg digesting shouldn't show up unless veg is researched, or toxic slurry isn't available until gold smelting) -- there are quite a few of these

the code should either happen on load of game (if it's C#) to ensure mod authors got it right too, or if it's a script, output/modify the C# code so that the tree is fully correct.

what can I do to help?

also, there are some things that I'd like to move around in the tree as well, like:

• sugar cane processing shouldn't need lab 4 cause making ethanol has been around since the moon has been shining (though antibiotics prolly should require lab 4)
• concrete mixer 3 doesn't need basic computing and can be put in construction 4
• sausage production prolly doesn't need lab 4 either (the spanish and germans have been doing it since at least 2kya)