I can confirm all your problems. I've corrected the sources and, finally, was able to install the forum.
Again: Thank you for your work.
Can you check the sources of the master branch?
I can confirm, that your solutions are a par with my own changes that I made during debugging the installation script. I also can confirm that I was able to install the forum with your code changes. In the light of my last observation that the forum responded with a blank page after the successful installation (see the latest two paragraphs in my last posting) the question remains, what you changed outside the installation script to make your code work while mine failed.
Anyway. I will perform now a few last tests and will release a new version if encounter no surprise.
Trenne niemals Müll, denn er hat nur eine Silbe!