make sure to commit and close index-writer when updating index

git-svn-id: https://svn.apache.org/repos/asf/maven/indexer/branches/lucene-4.6@1575151 13f79535-47bb-0310-9956-ffa450edef68
Fix junit test for lucene 4 index merge behaviour

git-svn-id: https://svn.apache.org/repos/asf/maven/indexer/branches/lucene-4.6@1575152 13f79535-47bb-0310-9956-ffa450edef68