I installed a nice new v2.0 installation, and then I killed it again with the same file. I did change some things, apparently not the installation killer.
However, I think this time I have worked it out, and now have changed that file again. However, I now have v2.2.1. In attempting to add the page type to the same location, silverstripe-v2.2.1/mysite/code and flushing the database, absolutely nothing happens. It's as though Silverstripe doesn't see my file. I have checked the file extension and properties and cannot work out what is going on.
1. My problem was that I was placing it into mysite/code instead of tutorial/code. Why does that make a difference? Will that be problematic long term? How can I switch it back to mysite/code and mysite/templates?
2. I have also conquered the installation killer! :) My specialised page type now works! Yay! :)