- Remove some old proto2-based C#-only messages
- Remove the "build" directory which only contained out-of-date files
- Remove the csharp_namespace option from proto2 messages
- Change "Google.ProtocolBuffers" to "Google.Protobuf" in other messages
ProtoDump isn't currently useful, but will be when ToString emits JSON: fixed.
ProtoBench: deleted; we should reinstate when there's a common proto3 benchmark.
ProtoMunge: delete; not useful enough to merit fixing up.
Removed the [TestFixture] from ByteStringTest as Travis uses a recent enough version of NUnit.