Example or two of data files for future compatibility testing

As AVRO-160 (file format) and AVRO-135 (compression) have settled down, I'd like to check in examples of data files with specific data in them, and write tests against those checked-in files. The current tests for data files rely on code to generate the files, and then read them back, which is perfect for testing that an AVRO version is self-consistent, but doesn't help if we accidentally break compatibility. (This test would fail, for example, if someone changed the metadata key for the schema, say.)