Add preserve UnknownFields
Compare floating point values bitwise
Add auto-generated header to C# generated files

* Add auto-generated header to C# generated files

* regenerate C# protos

 Add unknown field support for csharp

With this in place, all tests should pass.

Fixes #3725.

* Factored Conformance test messages into shared test schema.

* Updated benchmarks to use new proto3 message locations.

* Fixed include path.

* Conformance: fixed include of Python test messages.

* Make maven in Rakefile use --batch-mode.

* Revert changes to benchmarks.

On second thought I think a separate schema for
CPU benchmarking makes sense.

* Try regenerating C# protos for new test protos.

* Removed benchmark messages from test proto.

* Added Jon Skeet's fixes for C#.

* Removed duplicate/old test messages C# file.

* C# fixes for test schema move.

* Fixed C# to use the correct TestAllTypes message.

* Fixes for Objective C test schema move.

* Added missing EXTRA_DIST file.

Add more JSON tests around underscores

This should fix the failures in the conformance tests - although
it highlights the problem that we need to do this when changing
the conformance.proto file...

JSON tests fail, as we're not using OriginalNameAttribute yet.

The conformance tests now use types which are part of src/google/protobuf, so we need to include src in the proto path.
The notes around "fix-ups" have been out of date for some time now.

Generated code changes for previous commit (basically InternalBuildGeneratedFileFrom => FromGeneratedCode)

Other changes are due to the well-known types changing without us regenerating.

Completely untested so far - easier to get started in VS and then transfer to Linux for tweaking...