Fix build to better support python3 releases.

git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1561801 13f79535-47bb-0310-9956-ffa450edef68
AVRO-1446. C#: Correctly handle system errors in RPC.  Contributed by David Taylor.

git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1561874 13f79535-47bb-0310-9956-ffa450edef68
AVRO-1445. Java: Fix protobuf support to correctly handle enums with default values.

git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1561875 13f79535-47bb-0310-9956-ffa450edef68
AVRO-1443. Java builder and record API improvements.

 - All builders (generic and specific) extend generic records
 - Specific record builders do NOT extend GenericRecordBuilder,
   but implement the generic record builders interface.
 - Introduce interfaces for indexed/generic record builders.
 - Introduce interfaces for immutable indexed/generic records.
 - Update velocity template to add the new methods required for builders.
 - Deleted FooBarSpecificRecord (apparently unused, no schema definition available).