1) Project files for different configurations - we're going to look at all this again, ideally to just have a single PCL-compatible build
2) ProtoGen - the C++ generator is now the only one we care about
3) Proto files - these are mostly duplicates (or older versions) of the ones in the common directories
(Having regenerated descriptor.proto relative to src, the earlier commented-out code checking that dependencies match may now be okay to uncomment again. Will experiment in later CLs.)
This commit includes changes to the C#-specific protos, and rebuilt versions of the "stock" protos.
The stock protos have been locally updated to have a specific C# namespace, but this is expected to change soon, so hasn't been committed.
Four areas are currently not tested:
1) Serialization - we may restore this at some point, possibly optionally.
2) Services - currently nothing is generated for this; will need to see how it interacts with GRPC
3) Fields beginning with _{digit} - see https://github.com/google/protobuf/issues/308
4) Fields with names which conflict with the declaring type in nasty ways - see https://github.com/google/protobuf/issues/309
1) Remove CSharpOptions
2) A new version of DescriptorProtoFile (with manual changes from codegen - it would otherwise be Descriptor.cs)
3) Turn off CLS compliance (which we'll remove from the codebase entirely; I don't think it's actually relevant these days)
4) Add "public imports" to FileDescriptor, with code broadly copied from the Java codebase.
Lots more changes to commit before it will build and tests run, but one step at a time...