Builds fail on Windows

[martindholmes]

In working on issue #261, which caused me to run the tests on Windows for the first time in ages, I discovered that the build fails on line 299 of build.xml with [xslt] Failed to process null right after it loads the tokenize.xsl stylesheet. I'm not sure what the cause it, but I don't know whether we ever actually got the build working on Windows at all; it also fails in the 1.4 branch. I don't know how important this is; anyone using Windows for this kind of work has probably already got the WSL installed. But if it turns out to be an easy fix, we might as well make it.