Merged revision(s) 1584883 from lucene/dev/trunk:
Make Exception more readable (those coming from -Dtests.directory=NonExistentDir). We have Rethrow calss for that!

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1584885 13f79535-47bb-0310-9956-ffa450edef68