Fix for issue - https://issues.cloudera.org/browse/CDK-473

- CSV file header used to generate avro schema can only be Alphanumeric ( as per computer science definition).
- Additional check added to make sure that csv header should strictly follow Alphanumeric standards.
Yeah sure Tom i will move create a new method in the org.kitesdk.data.spi.Compatibility class for validation.
My bad I was not aware of such type of validator class exists. Will keep in mind.