LUCENE-4944: Prepend 'v' to (currently numeric) id attributes for release sections, and fail with a nice message when encountering the same section more than once within a single release. (merged trunk r1470088)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1470092 13f79535-47bb-0310-9956-ffa450edef68