Correct an issue parsing bytes field from protobuf

com.google.protobuf.ByteString doesn't provide an implicit conversion
from ByteString to Binary primitive, so the above change is necessary to
detect ByteString, explicitly convert to byte[] with toByteArray()
method, and return that.
Unit tests for protobuf bytes change

Added bytes field to test protobuf and updated unit test classes.  Pig
unit test updated because it tests the schema and detects the new field.
Merge pull request #380 from bryanherger/master

Correct an issue with ByteString handling in Protobuf Serde