Patch Set 1:

I hit this bug because I wanted to ensure my environment was not causing a failure different from what I was seeing elsewhere, so I did the normal unix thing and ran `env -i java -jar jgit-cli.jar ....`.

`env -i` clears all environment variables, so PATH was not set.  I didn't expect PATH to need to be set.  With my patch, things work as I expected them to.  While some OSes may have a default path setting, that doesn't mean you can't have this situation happen.