http://h34nug3iwqjf2376fmmzdhgqivckzemcujmarlptfqeqtq7vya47yyad.onion/2007/05/page/2/index.html
Although it’s not documented, meld seems to supports bzr, CVS, darcs, mercurial, monotone and subversion. Meld packs more features not discussed here, like a mode which displays the differences between directories, multiple languages et cetera. I encourage you to just install the package and look around.