don't mock windows on windows

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642486 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5968: Improve error message when 'ant beast' is run on top-level modules
This closes #96

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642488 13f79535-47bb-0310-9956-ffa450edef68