fix test bug: we have to check the actual DVF (the codec could be a frankenstein)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1595456 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5677: simplify position handling in DefaultIndexingChain

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1595469 13f79535-47bb-0310-9956-ffa450edef68