COMPRESS-285 use a volatile enum rather than an AtomicInteger

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1618584 13f79535-47bb-0310-9956-ffa450edef68
never meant to commit this, oops

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1618587 13f79535-47bb-0310-9956-ffa450edef68