use URLDecoder.decode() to unescape test resource paths

This is a fix for the build error described [here](https://groups.google.com/forum/#!topic/opentripplanner-dev/Ys9s3bX9eMs) and [here](https://groups.google.com/forum/#!topic/opentripplanner-dev/WcvSXGvWp_E).

If the repository was installed on a path containing a folder with a space in the name, some test resources failed to open.

The fix is based on http://stackoverflow.com/questions/3263560/sysloader-getresource-problem-in-java.