Merge -r 1640178:1640179 from trunk to branch. Fixes: AVRO-1596. AVRO-834. Java: Data File corruption recovery tool. Contributed by scottcarey and tomwhite.

git-svn-id: https://svn.apache.org/repos/asf/avro/branches/branch-1.7@1640181 13f79535-47bb-0310-9956-ffa450edef68