avro

AVRO-1138. C: Open data file with new block size

This obviously won't affect any blocks that are already in the file, but any new
blocks that are appended will use the new block size.


git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1384531 13f79535-47bb-0310-9956-ffa450edef68