Well, the background of my question is this: I don't have a build tree of
master, and I don't intend to get one, either. I'm just trying to do what's
necessary to have my own project running on Windows, and to fix the bugs that
affect it, or that I happen to stumble upon, along the way.

I do not intend to dive head first into the KDE on Windows project. I already
have my own pet project, thank you. Building several branches, and possibly
even with several compilers per branch is a no-go to me.

Projects usually have CI for several tier testing. The KDE Windows project also has several builds run automatically on a server:

http://www.winkde.org/pub/kde/ports/win32/dashboard/
 
So that's why I'm asking about policy, here: If I cannot (be convinced to)
test a patch in master, but I think it should go there, how should I proceed.

The problem is that you think, but you do not know. I understand your good intention and I appreciate that, but unfortunately that is not alway enough if it causes breakages for others.
 
Reviewboard? This list?

You will need to find another contributor somehow who will know. The generic rules applies here: irc, mailing list, review board, and so forth.

I do not personally have time to check your write up now, but thank you for your contribution.

Laszlo