Fix to read a new avro schema...
Make setting requested projection and avro schema more independent, so that
you only need to set the Avro schema if it is different to the
writer's schema.
Support promotion of int, long and float to wider types.

This is specified in http://avro.apache.org/docs/current/spec.html#Schema+Resolution
Use a default Avro read schema when none specified in Parquet-Avro.
Add tests for reading Parquet files using the default
Avro schema.
Minor changes following Julien's review
Revert change making field final that failed compatibility test.
Merge pull request #282 from tomwhite/avro-default-read-schema

Avro default read schema