The valueOf method on enums is deprecated, but for compatibility reasons
the generated code has to keep using it. We can use an annotation to
suppress the deprecation warnings.

* Add auto-generated header to C# generated files

* regenerate C# protos

 Add unknown field support for csharp

Fixes https://github.com/google/protobuf/issues/3268

This fixes issue #1775.

Make it clear default value is only omitted for proto3.

Clarify that JSON parser are required to accept both UTC and other
timezone offsets.

Fixes issue 3093

This is necessary for avoiding a strange compiler error that we have
already run into with older versions of Clang on NaCl.

This removes a Visual Studio warning:

warning C4146: unary minus operator applied to unsigned type, result
still unsigned.

unittest_proto3 had been changed in a very backward-incompatible
way which was never going to work with C# as it imports proto2 messages.

This is now a copy of the old file, but with a package name change for
compatibility with the remaining files in src/google/protobuf.

The other moves are for files that are only used by C#.

- Removed the redefination in the atomicword_compat.h. Now Atomic32 will
alwyas be intptr_t in 32bit platforms, the bridge is no longer needed.
- Change NaCl 64bit to use intptr_t instead of int32 for Atomic32,
otherwise AtmoicWord APIs will miss the definations.

After this change, the AtmoicWord will always be either Atomic32 or
Atmoic64 depending on the platforms.

If messages A and B have the same oneof case, which is a message
type, and we merge B into A, those sub-messages should be merged.

Fixes #3200.

Note that I haven't regenerated all the code, as some of the protos
have been changed, breaking generation.

* Reserve unknown in ruby

* Revert ruby tests. Wait for cpp impl for conformance test

* Add conformance test for preserving unknown

* Add unknown field conformance test to csharp failure list.

* Fix comments

* Fix comment

* Fix comments

* Fix typo

* Use stringsink_string directly

* Mark hd unused

* Remove unused encodeunknown_handlerfunc

See https://github.com/google/protobuf/issues/3752 for context.

fixes #3700

* Use constexpr more with VC++ 2017

Chrome's official builds have over 170 dynamic initializers for
variables of the form *::TableStruct::aux. Defining
PROTOBUF_CONSTEXPR_VAR to be constexpr for VS 2017 gets rid of all of
these and saves about 10 KB of binary size.

* Update generated_message_table_driven.h

Restore accidentally deleted line.