* Enable ignoring unknown in json parsing in php

* Update generated descriptor files

* Update failure list for other languages.

* Remove unnecessary php files

* Remove protoc conditional properties

* Fix duplicate brace

This potentially avoids compiler warnings.

* Added props to C# tools

* Add targets file to makefile.am

Add mention to the "Build" section of the ReadMe of the requirement of installing an optional component to VS2017.

With this fix, Unity using IL2CPP should work with one of two
approaches:

- Call `FileDescriptor.ForceReflectionInitialization<T>` for every
  enum present in generated code (including oneof case enums)
- Ensure that IL2CPP uses the same code for int and any int-based
  enums

The former approach is likely to be simpler, unless IL2CPP changes
its default behavior. We *could* potentially generate the code
automatically, but that makes me slightly uncomfortable in terms of
generating code that's only relevant in one specific scenario. It
would be reasonably easy to write a tool (separate from protoc) to
generate the code required for any specific set of assemblies, so
that Unity users can include it in their application. We can always
decide to change to generate it automatically later.

* Edited MessageFieldGenerator to clone to backing field instead of property

* Generated C# proto code

The SampleEnumMethod method was previously only called via
reflection, so the Unity linker thought it could be removed. Ditto
the parameterless constructor in ReflectionHelper.

This PR should avoid that issue, reducing the work needed by
customers to use Google.Protobuf from Unity.

* Fix setup.py for windows build.

* Bump version number to 3.5.2

* Cat the test-suite.log on errors for presubits

For oneofs, to get the case, we need to call the property that
returns the enum value. We really want it as an int, and modern
runtimes allow us to create a delegate which returns an int from the
method. (I suspect that the MS runtime has always allowed that.)
Old versions of Mono (e.g. used by Unity3d) don't allow that, so we
have to convert the enum value to an int via boxing. It's ugly, but
it should work.

This should work on Unity, Mono and .NET 3.5 as far as I'm aware.
It won't work on platforms where reflection itself is prohibited,
but that's a non-starter basically.

Updated NUnit packages, removed NUnitLite added packages for dotnet and Visual Studio, changed dotnet command in buildall to dotnet test, and deleted Program.cs (because it's no longer required).

Increased `CodedInputStream.DefaultSizeLimit` to `Int32.MaxValue` to make it consistent with the Java implementation.

This will allow SourceLink as per #4179, and mean that we can use C#
7.0 language features in the library (but not in generated code).
This does not affect which platforms we're *targeting*, so end users
won't see any difference.

It would be nice to update to 2.1.4, but AppVeyor's "Visual Studio
2017" environment is only 2.0.3.

By default, unknown fields are preserved when parsing. To discard
them, use a parser configured to do so:

var parser = MyMessage.Parser.WithDiscardUnknownFields(true);

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.

This is the manual code part of the Google.Protobuf library, and tests.
Some tests will fail until codegen is changed and rerun.

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#.