Failing `ValidData*` conformance tests

[garyp]

These conformance tests fail on all platforms, so most likely it's a bug in the pbandk code:

Recommended.Proto2.ProtobufInput.ValidDataOneofBinary.MESSAGE.Merge.ProtobufOutput
Recommended.Proto3.ProtobufInput.ValidDataOneofBinary.MESSAGE.Merge.ProtobufOutput
Required.Proto2.ProtobufInput.ValidDataMap.STRING.MESSAGE.MissingDefault.JsonOutput
Required.Proto2.ProtobufInput.ValidDataOneof.MESSAGE.Merge.JsonOutput
Required.Proto2.ProtobufInput.ValidDataOneof.MESSAGE.Merge.ProtobufOutput
Required.Proto3.ProtobufInput.ValidDataMap.STRING.MESSAGE.MissingDefault.JsonOutput
Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.JsonOutput
Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.ProtobufOutput