LUCENE-5341: automate default codec package extraction for use in the generated Lucene documentation's link to the index file format documentation (merged branch_4x r1542013)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1542018 13f79535-47bb-0310-9956-ffa450edef68
- Move 'upgrading from previous version' section above the 'detailed change list' super-section
- Put parens around 'Elran Dvir via Erick Erickson' so that it gets recognized as an attribution
(merged branch_4x r1542021)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1542022 13f79535-47bb-0310-9956-ffa450edef68