scalatest ant task path resolution

If I specify a in my
build.xml, the scalatest task seems to resolve the name relative to
the directory ant was started in (with ant -find build.xml), not
relative to the directory the build.xml is located in, as are all other
paths in ant. This means that you have to go hunting for the log files
after every compile if have more the one subdirectory for your sources.

- Florian.