so i got a little work done today on subversion's cancelation support. i've become more and more convinced that this is going to be a pain in the ass, but it's something that has to be done, so i should probably stop bitching about it and just do it already.
anyway, i can now do a repos-repos diff and cancel it part way through via control-c, and it seems to work just fine, so i can at least feel like i've accomplished something.
now i just need to decide if the technique i'm using for this is going to be 'the right one', and if so, start applying it to the rest of the tree, since there are like a million other places that need the same kind of attention as repos-repos diffs.