Upgrade of diagxy

I have just posted a minor upgrade of diagxy. At the suggestion of a graduate student at Kent State named Gerd Zeibig, I have added a new feature that allows to identify nodes of a diagram with short identifiers and then draw arrows between those nodes. He had implemented this and asked me what I thought. I found a simpler way than he (he had defined over 100 new counters and the number of counters that tex allows is 256, so they are considered a rare commodity; my code uses only 2 new counters). This kind of reintroduces the matrix mode except with absolute positioning of the vertices. The results are found, as usual, in ftp.math.mcgill.ca/pub/barr/diagxy.zip.